// There is nothing in a caterpillar that tells you its going to be a butterfly --------------------- !
#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
#define ll long long int
#define pi pair<int,int>
#define pii pair<ll,pi>
#define f first
#define mp make_pair
#define mod 1000000007
#define s second
#define pb push_back
int main(){
int t;
cin >> t;
while(t--){
ll F,H,W,x;
cin >> F >> H >> W;
vector<ll>cuts;
rep(i,F){
cin >> x;
cuts.pb(x);
}
cuts.pb(0);
cuts.pb(W);
sort(cuts.begin(),cuts.end());
ll ans=INT_MAX;
for(int i=1;i<cuts.size();i++){
ans=min(ans,cuts[i]-cuts[i-1]);
}
ans*=H;
cout<<ans<<"\n";
}
}
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