import java.io.*;
import java.util.*;

class Truck {
    int st,f;
    public Truck(int st, int f) {
        this.st=st; this.f=f;
    }
    int getST(){ return st; }
    int getF() { return f; }
}
class TCmp implements Comparator<Truck> {
    public int compare(Truck t1, Truck t2) {
        if(t1.st<t2.st) return -1;
        else if(t1.st>t2.st) return 1;
        else return 0;
    }
}
class Code
{
    static class Reader
    {
        final private int BUFFER_SIZE = 1 << 32;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            }  while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        }
    }

    static void display(List<Truck> t) {
        for(int i=0;i<t.size();i++) out.println(t.get(i).getST()+" "+t.get(i).getF());
        out.println();
    }

    static PrintStream out = new PrintStream(System.out);
    public static void main(String[] args)throws IOException {
        //try {
            Reader sc = new Reader();
            PrintWriter out = new PrintWriter(System.out);
            //BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            int tc=sc.nextInt();//Integer.valueOf(br.readLine());
            while(tc-->0) {
                int n=sc.nextInt(),stp[]=new int[n],fuel[]=new int[n];
                List<Truck> list = new ArrayList<>();
                for(int i=n-1;i>=0;i--) {
                    stp[i]=sc.nextInt();
                    fuel[i]=sc.nextInt();
                }
                int L=sc.nextInt(),P=sc.nextInt();
                if(P>=L) { out.println(0); continue; }
                for(int i=0;i<n;i++) list.add(new Truck(L-stp[i],fuel[i]));
                Collections.sort(list,new TCmp());
                //display(list);
                PriorityQueue<Integer> pQ=new PriorityQueue<>(Collections.reverseOrder());
                long cfl=P;int ct=0,i=0;
                boolean b=false;
                for(;cfl<L;) {
                    if(list.get(i).getST()>cfl) {
                        while(!pQ.isEmpty() && list.get(i).getST()>cfl) { cfl+=pQ.poll(); ct++; }
                        if(list.get(i).getST()>cfl || cfl>=L) break;
                    }
                    while(i<n && list.get(i).getST()<=cfl) pQ.add(list.get(i++).getF());
                    cfl+=pQ.poll();
                    ct++;
                    //out.println(cfl+" "+ct);
                    //if(cfl>=L) break;
                }
                out.println((cfl<L)?-1:ct);
            }
            //out.println("");
            out.flush();
            out.close();

        //} catch(Exception e) {}
    }
}