UVA 10014

#include<iostream>
#include<iomanip>
using namespace std;
#define MAXN 10010
int main()
{
    double c[MAXN];
    double a,b;
    int cases,n;
    cin>>cases;
    while(cases--)
    {
        cin>>n>>a>>b;
        double sum=0,tmp=0;
        for(int i=0;i<n;i++)
        {
            cin>>c[i];
        }
        tmp=0;
        for(int i=0;i<n;i++)
        {
            tmp+=c[i];
            sum+=tmp;
        }
        cout.setf(ios::fixed);
        cout<<setprecision(2)<<((b+(n)*a-2*sum)/(n+1))<<endl;
        if(cases!=0)
        cout<<endl;
        
    }
    return 0;
}