#include<bits/stdc++.h>
using namespace std;
#define ll long long int 
int main()
{
    ll tc;
    cin>>tc;
    while(tc--)
    {
       ll n,k,x;
        cin>>n>>k>>x;
        
        vector<ll>v(n);
        for(int i=0;i<n;i++)
        {
            cin>>v[i];
        }
        ll s=0,id=-1,mx=-1,z=0;
        for(int i=0;i<k;i++)
        {
            s+=v[i];
            if(v[i]==0) z++;
        }
        if(s%x == 0 && z== 0) {
        mx= 1;
        id = 0;
    }

    for (int i=k;i<n;i++) {
        s-= v[i-k];
        if(v[i-k]==0) z--;

        s+=v[i];
        if(v[i]==0) z++;

        if (s%x == 0) {
        ll f=(z==0) ? 1 : 0;
            
            if (f>mx) {
                mx=f;
                id=i-k+1;
            }
        }
    }
    if(id==-1)
        cout<<-1<<endl;
        else
            cout<<id+1<<endl;
    }
}