#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef pair<int,int> PII;
const int N=1e5+10,M=2*N;
const int mod=998244353;
const LL P=1e9+7;
const LL INF=1e18;
int h[N],e[M],ne[M],w[M],idx;
int dfn[N], low[N], timestamp;
int stk[N], top;
bool in_stk[N];
int id[N], scc_cnt, Size[N];
int dout[N];
int T=1;
int d[N][2];

void add(int a,int b){
    e[idx]=b,ne[idx]=h[a],h[a]=idx++;
}



void tarjan(int u)
{
    dfn[u] = low[u] = ++ timestamp;
    stk[ ++ top] = u, in_stk[u] = true;
    for (int i = h[u]; i != -1; i = ne[i])
    {
        int j = e[i];
        if (!dfn[j])
        {
            tarjan(j);
            low[u] = min(low[u], low[j]);
        }
        else if (in_stk[j]) low[u] = min(low[u], dfn[j]);
    }

    if (dfn[u] == low[u])
    {
        ++ scc_cnt;
        int y;
        do {
            y = stk[top -- ];
            in_stk[y] = false;
            id[y] = scc_cnt;
            Size[scc_cnt] ++ ;
        } while (y != u);
    }
}



void solve(){
    int n;
    cin>>n;
    LL res=0;

    vector<int> h(n),p(n);

    for(int i=0;i<n;i++) cin>>h[i];
    for(int i=0;i<n;i++) cin>>p[i];

    vector<PII> q;

    for(int i=0;i<n;i++){
        if(h[i]>p[i]){
            cout<<-1<<endl;
            return;
        }

        q.push_back({p[i]-h[i],p[i]});
    }


    sort(q.begin(),q.end());


    for(int i=1;i<n;i++){
        if(q[i].second<q[i-1].second){
            cout<<-1<<endl;
            return;
        }
    }

    cout<<q[n-1].first<<endl;
}





 
int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    //int T=1;

    cin>>T;
    //T=10000;
    while(T--) solve();
 
    return 0;
}