def slow(n, k, a, b):
    # n / (n + y) >= a / b
    # b n >= a (n + y)
    # b n >= a n + a y
    # (b - a) n / a >= y
    d = b - a
    steps = 0
    while k > 0:
        steps += 1
        y = min(k, d * n // a)
        if y == 0:
            break
        k -= y
        n += y

    if k:
        return -1
    else:
        return steps


def main():
    t = int(input())
    for _ in range(t):
        n, k, a, b = map(int, input().split())
        print(slow(n, k, a, b))


if __name__ == "__main__":
    main()