#include <bits/stdc++.h>
using namespace std;
#define int long long 
const int oo = 1'000'000'000'000'000'000ll;
int n,k,X,Y;
vector<int>xs,ys;
int sumx,sumy;
unordered_map<int,int>memo;
int getmin(int rounds){
	if(memo.find(rounds) != memo.end())return memo[rounds];
	int hx=sumx*rounds,hy=sumy*rounds;
	int curdiff=abs(hx-X)+abs(hy-Y);
	int idx=rounds*n;

	if(curdiff<=k*idx)return idx;
	for(int i=0;i<n;i++){
		hx+=xs[i];
		hy+=ys[i];
		int curdiff=abs(hx-X)+abs(hy-Y);
		int idx=rounds*n+i+1;
		if(curdiff<=k*idx)return idx;
	}
	return oo;
}
void solve(){
	cin>>n>>k>>X>>Y;
	xs.clear();ys.clear();
	memo.clear();
	sumx=0;sumy=0;
	for(int i=0;i<n;i++){
		int v1,v2;cin>>v1>>v2;
		sumx+=v1;sumy+=v2;
		xs.push_back(v1);
		ys.push_back(v2);

	}

	if(X==0&&Y==0){
		cout<<0<<"\n";
		return;
	}
	int hx=0,hy=0;
	int ans=getmin(0);
	for(int i=0;i<n;i++){
		hx+=xs[i];
		hy+=ys[i];
		
		if(sumx && sumy){
			int difx=X-hx;
			int numx=difx/sumx;
			int dify=Y-hy;
			int numy=dify/sumy;

			if((numx==numy) && numx>=0 && (difx%sumx==0) && (dify%sumy==0)){
				ans=min(ans,numx*n+i+1);
			}
		} else if(sumx){
			int difx=X-hx;
			int numx=difx/sumx;

			int dify=Y-hy;
			if(dify==0 &&(numx >= 0) && (difx%sumx==0)){
				ans=min(ans,numx*n+i+1);
			}
		} else if(sumy){
			int difx=X-hx;
			int dify=Y-hy;
			int numy=dify/sumy;

			if(difx==0&&(numy>=0) && (dify%sumy==0)){
				ans=min(ans,numy*n+i+1);
			}
		} 
	}
	if(ans==oo)ans=-1;
	cout<<ans<<"\n";
}
int32_t main(){
	ios_base::sync_with_stdio(0);cin.tie(0);
	int T; cin>>T;
	while(T--)solve();
}