RCC Qual 3 Task B

t = int(input())
for t_i in range(t):
    n, H, A = map(int, input().split())
    p = []
    for i in range(n):
        h, a = map(int, input().split())
        x = h // A
        if h % A != 0:
            x += 1
        p.append([h, a, x * a])
    p = sorted(p, key = lambda item: item[2], reverse = True)
    res = None
    for i in range(n):
        a1 = H // p[i][1]
        if H % p[i][1] != 0:
            a1 += 1
        a2 = p[i][0] // A
        if p[i][0] % A != 0:
            a2 += 1

        if a1 < a2:
            H = H - p[i][1] * a1
            p[i][0] = p[i][0] - A * a1
        else:
            H = H - p[i][1] * a2
            p[i][0] = p[i][0] - A * a2
        if H <= 0:
            res = i
            break
    if res == None:
        print (-1)
    else:
        print (res)