#include<bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define newl cout<<"\n";
#define space cout<<" ";
#define sz(x) x.size()
#define NumOfDigit(w) log10(w) + 1
#define MOD 1'000'000'007
#define inf 2'000'000'000
#define PI 3.141592654
#define modulo(a, b, mod) ((((a) % (mod)) + ((b) % (mod))) % (mod))
#define ceil(w, m) (((w) / (m)) + ((w) % (m) ? 1 : 0))
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define cin(v) for (auto&i:v) cin >> i;
#define cout(v) for (auto&i:v) cout << i << " ";
#define fixed(n) fixed << setprecision(n)
using namespace std;
void zainab_hamdy(){
  ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
 //freopen("collisions.in" , "r" ,stdin);
  #ifndef ONLINE_JUDGE
     freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
 #endif

}
ll gcd(ll a, ll b){
    while(b) {
        a %= b;
        swap(a, b);
    }
    return a;
}
int main(){
zainab_hamdy();
int t; cin>>t;
while(t--){
    int n,sum,sum1=0; cin>>n>>sum;
    vector<int> v(n);
    for(int i=0;i<n;i++) {
        cin>>v[i];
        sum1+=v[i];
    }
    if(sum> sum1){
        cout<<"-1\n";
        continue;
    }
    int pre[n+2]{};
for(int i=1;i<n+1;i++){
    pre[i]=pre[i-1]+v[i-1];

}
/*
for(int i=1;i<n+1;i++){
    cout<< pre[i]<<" ";

}newl*/
int idx=0;
for(int i=0;i<n/2 +1;i++){

    if(pre[n-idx]-pre[idx]== sum){
      //  cout<<pre[n-idx] <<" "<< pre[idx] <<"   ";
   cout<<idx<<"\n";
    break;
   }
   else idx++;
}

}
 return 0;
}