#include <bits/stdc++.h>
using namespace std;
 
#define int long long
void solve(){
	int n,c;
	cin>>n>>c;
	vector<int> v(n);
	for(int i=0;i<n;i++){
		cin>>v[i];
	}
	int a=0;
	for(int i=0;i<n;i++){
		a+=(v[i]*v[i]);
	}
	int b=0;
	for(int i=0;i<n;i++){
		b+=v[i];
	}
	int k=b;
	a=n*(a-c);
	b=(b*b);
	int k2=sqrt(b*b-a);
	cout<<(k2-b)%n+((k2-b)/n)<<endl;
 
 
 
 
 
}
signed main() {
	// your code goes here
	int t;
	cin>>t;
	while(t--){
		solve();
	}
	return 0;
}

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