#include <bits/stdc++.h>

#define icin(x) scanf("%d",&x)
#define pb push_back
#define LL long long
#define F first
#define S second
#define eps ((double)1e-14)
#define maxn 109
#define maxm 100009

using namespace std;

vector<double> vec;
double f(double r)
{
  double ans = 0;
  int cur = 1;
  for(int i=0;i<vec.size();i++)
  {
    ans += (vec[i])/pow((1+r),cur);
    cur++;
  }
  return ans;
}

int main()
{
  int t;
  icin(t);
  for(int tc=1;tc<=t;tc++)
  {
    int m;
    icin(m);
    int s;
    cin >> s;
    vec.clear();
    for(int i=0;i<m;i++)
    {
      int x;
      icin(x);
      vec.pb((double)x);
    }
    double lo=-1,hi=1;
    double k;
    for(int i=1;i<=5000;i++)
    {

       k = (lo+hi)/2;
     // cout << k << " " ;
      if(f(k)>s)
        lo=k;
      else
        hi=k;
    }

    printf("Case #%d: %.20lf\n",tc,k);
  }

}