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

#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define pb push_back
#define x first
#define y second
#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)

typedef long long ll;
typedef double db;
typedef long double LD;
typedef pair<int, int> pii;
typedef pair<db, db> pdd;
typedef pair<ll, ll> pll;


int solve()
{
	ll n, k, a, b;
	if (!(cin >> n >> k >> a >> b))
		return 1;
	
	if (n * (b - a) < a)
	{
		cout << "-1\n";
		return 0;
	}
	
	int ans = 0;
	while (k)
	{
		ans++;
		ll y = (n * (b - a)) / a;
		//cerr << "y = " << y << '\n';
		if (y == 0)
		{
			cout << "-1\n";
			return 0;
		}
		//y = abs(y);
		k -= y;
		n += y;
		k = max(0LL, k);
	}
	
	cout << ans << '\n';
	
	return 0;
}

int32_t main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	int TET = 1e9;
	cin >> TET;
	for (int i = 1; i <= TET; i++)
	{
		if (solve())
		{
			break;
		}
		#ifdef ONPC
			cerr << "_____________________________\n";
		#endif
	}
	#ifdef ONPC
		cerr << "\nfinished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec\n";
	#endif
	return 0;
}