#include <iostream>
#include <algorithm>
#define PII pair<int,int>

using namespace std;

const int N=1e5+5;

int t,n,h[N],p[N];
PII a[N];

int main(){
	ios::sync_with_stdio(0),cin.tie(0);
	cin>>t;
	while (t--){
		cin>>n;
		for (int i=1;i<=n;i++) cin>>h[i];
		for (int i=1;i<=n;i++) cin>>p[i];
		bool ok=1;
		for (int i=1;i<=n;i++)
			ok&=h[i]<=p[i];
		if (!ok){
			cout<<"-1\n";
			continue;
		}
		for (int i=1;i<=n;i++)
			a[i]={h[i],p[i]-h[i]};
		sort(a+1,a+n+1);
		ok=1;
		for (int i=1;i<n;i++)
			if (a[i].second>a[i+1].second) ok=0;
		if (!ok) cout<<"-1\n";
		else cout<<a[n].second<<"\n";
	}
	return 0;
}