Maximzize

#include <bits/stdc++.h>
using namespace std;
#define PB push_back
#define ZERO (1e-10)
#define INF (1<<29)
#define CL(A,I) (memset(A,I,sizeof(A)))
#define DEB printf("DEB!\n");
#define D(X) cout<<"  "<<#X": "<<X<<endl;
#define EQ(A,B) (A+ZERO>B&&A-ZERO<B)
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef pair<int,int> ii;
typedef vector<ii> vii;
#define IN(n) int n;scanf("%d",&n);
#define FOR(i, m, n) for (int i(m); i < n; i++)
#define REP(i, n) FOR(i, 0, n)
#define F(n) REP(i, n)
#define FF(n) REP(j, n)
#define FT(m, n) FOR(k, m, n)
#define aa first
#define bb second
void ga(int N,int *A){F(N)scanf("%d",A+i);}
#define MX (1<<17)
int N,K,A[MX],B[MX];
ll S[MX],T,H;
#define CK(A) H=max(H,A)
void ts(ll T,ll a,ll b){
    CK(T+(a+K)*b);
    CK(T+(a-K)*b);
}
int main(void){
    IN(tt)F(tt){
        scanf("%d%d",&N,&K);
        ga(N,A),ga(N,B),T=0;
        F(N)T+=S[i]=A[i]*1ll*B[i];
        H=T;
        F(N)ts(T-S[i],A[i],B[i]);
        printf("%lld\n",H);
    }
    return 0;
}