#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pb push_back
#define eb emplace_back
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define SZ(x) ((int)(x).size())
typedef vector<int> VI;
typedef long long ll;
typedef pair<int,int> PII;
const ll MOD=1e9+7;
// head

const int N=1e5+10;
struct node
{
	int a,b;
}a[N];

signed main() 
{
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
	
	int t; cin>>t;
	while (t--) {
		int n;cin>>n;
		for(int i=1;i<=n;++i) cin>>a[i].a;
		for(int i=1;i<=n;++i) cin>>a[i].b;
		bool f=false;
		int k=0;
		for(int i=1;i<=n;++i) {
			if(a[k].a<a[i].a) k=i;	
			if(a[i].b<a[i].a) {
				cout<<"-1\n";
				f=true;
				break;
			}
		}
		if(f) continue; 
		f=false;
		for(int i=1;i<=n;++i) {
			if(a[i].a<a[k].a&&a[i].b>a[i].b) {
				f=true;
				cout<<"-1\n";
				break; 
			} 
		}
		if(f) continue;
		int ans=0;
		for (int i=1;i<=n;++i) {
			ans=max(ans,a[i].b-a[i].a);
		}
		cout<<ans<<'\n';
	}
}