import math
def eq(a,b,c):
x=b**2-(4*a*c)
y=math.sqrt(x)
ans=(-b+y)/(2*a)
return ans
t=int(input())
for i in range(0,t):
x=0
y=0
nn,kk=input().split()
n=int(nn)
k=int(kk)
li=list(map(int,input().split(' ')))
for j in li:
x+=j
y+=j**2
a=4*n
b=4*x
c=y-int(k)
ans=eq(a,b,c)
an=int(ans)
print(f"{an}\n")
#include "bits/stdc++.h"
using namespace std;
#define ll long long
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(),v.rend()
#define pb push_back
#define sz(a) (int)a.size()
#define int long long
void solve() {
int n, c; cin >> n >> c;
vector<int> a(n);
for(int i = 0; i < n; ++i) cin >> a[i];
int l = 1, r = 1e9;
while(l <= r) {
int mid = l + (r - l) / 2;
int sumall = 0;
for(int i = 0; i < n; ++i) {
sumall += (a[i] + 2 * mid) * (a[i] + 2 * mid);
if(sumall > c) break;
}
if(sumall == c) {
cout << mid << "\n";
return;
}
if(sumall > c) {
r = mid - 1;
} else {
l = mid + 1;
}
}
}
int32_t main() {
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
int t = 1;
cin >> t;
while(t--) {
solve();
}
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