#include <bits/stdc++.h>
using namespace std;
int main() {
// your code goes here
int q;
cin>>q;
while(q--)
{
int n,t;
cin>>n>>t;
int d[n],c[n],j=0;
for(int i=0;i<n;i++) cin>>d[i];
for(int i=0;i<n;i++) cin>>c[i];
int count=0,temp=0;
for( j=0;j<n;j++)
{
if((j+d[j]<t))
{
count=max(count,c[j]);
if(c[j]>=count)
{
continue;
}
}
}
cout<<j+1<<"\n";
}
return 0;
}
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