#include<iostream>
using namespace std;
int main()
{
    //freopen("input2.txt","r",stdin);
    //freopen("output2.txt","w",stdout);
    int t,n,d,sum,tot_time,jokes;
    cin>>t;
    while(t--)
    {
              sum=0;
              cin>>n>>d;
              int time[n];
              for(int i=0;i<n;i++)
              {
                      cin>>time[i];
                      sum=sum+time[i];
              }
              tot_time=(n-1)*10+sum;    //minimum time required in tasting all the dishes including rest 
              if(tot_time<=d)
              {
                             jokes=(d-sum)/5;
                             cout<<jokes<<endl;
              }
              else
                  cout<<"-1"<<endl;
    }
    return 0;
}              

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MgozIDMwCjIgMiAxCjMgMjAKMiAxIDE=

2
3 30
2 2 1
3 20
2 1 1