#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 long 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;
	}
	
	auto check = [&](ll tr) -> bool
	{
		db dr = pow((b * 1. / a), tr);
		//ll cil = floor(dr);
		return n * 1. * dr >= n + k;
	};
	
	ll l = 0, r = 1e9 + 47;
	while (r - l > 1)
	{
		ll mid = (l + r) / 2;
		if (check(mid))
			r = mid;
		else
			l = mid;
	}
	cout << r << '\n';
	
	//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;
}