#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define ALL(v) v.begin(),v.end()
#define dbg(x) cerr << #x << ": " << (x) << endl;

int n;
vector<int> h,p;
vector<int> d(1e6+1,-1);

void solve() {
    cin >> n;
    h.resize(n);
    p.resize(n);
    for (int i = 0; i < n; ++i) cin >> h[i];
    for (int i = 0; i < n; ++i) cin >> p[i];

    vector<int> ord(n);
    iota(ALL(ord),0);
    sort(ALL(ord), [&](int i, int j) {
        return p[i] < p[j];
    });
    
    bool ok = true;
    for (int i = 0; i+1 < n; ++i) {
        int x = ord[i];
        int y = ord[i+1];
        int dx = p[x]-h[x];
        int dy = p[y]-h[y];
        if (dx < 0 || dy < 0) {
            ok = false;
            break;
        }

        if (p[x] == p[y]) {
            if (h[x] != h[y] || dx != dy) {
                ok = false;
                break;
            }
        }
        else if (h[x] > h[y] || dx > dy) {
            ok = false;
            break;
        }
    }
    int ans = -1;
    if (ok) {
        ans = p[ord.back()] - h[ord.back()];
    }

    cout << ans << '\n';

    // clean
    for (int i : p) d[i] = -1;
}

int main() {
    int t;
    cin >> t;
    while (t--) solve();
}