#include <bits/stdc++.h>
using namespace std;

#define pb push_back

using ll = long long;

int TC, n, k, x, y, x_0[100005], y_0[100005];
ll sum_x, sum_y, pf_x, pf_y, ans = LLONG_MAX;

void solve() {
	cin >> n >> k >> x >> y;
	for (int i = 0; i < n; i++) {
		cin >> x_0[i] >> y_0[i];
		sum_x += x_0[i];
		sum_y += y_0[i];
	}
	for (int r = 0; r < n; r++) {
		ll a = x - pf_x;
		ll b = y - pf_y;
		ll lo = 0;
		ll hi = (ll)1e12;
		while (lo <= hi) {
			ll mid = (lo + hi) / 2;
			ll oth_x = mid * sum_x;
			ll oth_y = mid * sum_y;
			ll val = llabs(a - oth_x) + llabs(b - oth_y);
			if ((val + k - 1) / k <= (mid * n + r)) {
				ans = min(ans, mid * n + r);
				hi = mid - 1;
			} else {
				lo = mid + 1;
			}
		}
		pf_x += x_0[r];
		pf_y += y_0[r];
	}
	cout << (ans == LLONG_MAX ? -1 : ans) << '\n';
	sum_x = sum_y = pf_x = pf_y = 0;
	ans = LLONG_MAX;
}

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	cin >> TC;
	while (TC--) {
		solve();
	}
}