CHFM

#include<iostream>
using namespace std;
int main()
{
    long int t;
    cin>>t;
    for(int i=0;i<t;i++)
    {
        long int n;
        cin>>n;
        long int ar[n];
        long double s=0.0,avg=0;
        for(int j=0;j<n;j++)
        {
            cin>>ar[j];
            s=s+ar[j];
        }
        avg=(long double)s/n;
        
            int min=100000,l=-1;
            for(int j=0;j<n;j++)
            {
                if(ar[j]==avg)
                {
                    if(ar[j]<min)
                    {
                        min=ar[j];
                        l=j;
                    }
                }
            }
            
            if(l==-1)
             cout<<"Impossible"<<endl;
             else
            cout<<l+1<<endl;
        
    }
    return 0;
}
//https://www.codechef.com/problems/CHFM