/** gnu specific **/
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
/** contains everything I need in std **/
#include <bits/stdc++.h>

#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(S) ((int)S.size())
#define FOR(i, st_, n) for(int i = st_; i < n; ++i)
#define RFOR(i, n, end_) for(int i = (n)-1; i >= end_; --i)
#define x first
#define y second
#define pb push_back
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
typedef pair<double, double> pdd;
typedef unsigned long long ull;
typedef long double LD;
typedef pair<ull, ull> pull;
using namespace __gnu_pbds;
typedef tree<ll, null_type, less<>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
using namespace std;
#ifdef ONPC
mt19937 rnd(228);
#else
mt19937 rnd(chrono::high_resolution_clock::now().time_since_epoch().count());
#endif


int solve()
{
	ll n,k,a,b;
	if(!(cin>>n>>k>>a>>b))return 1;
	if(b*n < a*(n+1))
	{
		cout<<"-1\n";
		return 0;
	}
	ll y=(n*b-a*n)/a;
	ll res=0;
	//cout<<"y="<<y<<endl;
	for(; k > 0;)
	{
		ll x = (a*n + y*a + a - n*b + (b*y - y*a-1)) / (b*y - y*a);
		if(k-y*x < 0)
		{
			res += (k+y-1)/(y);
			break;
		}
		else
		{
			res += x;
			k -= y*x;
			n += y*x;
			y=max(y+1,(n*b-a*n)/a);
			//cout<<"dres="<<x<<endl;
		}
		//cout<<"y="<<y<<endl;
	}
	cout<<res<<'\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
        cout << "__________________________" << endl;
#endif
    }
#ifdef ONPC
    cerr << endl << "finished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec" << endl;
#endif
}