#include <bits/stdc++.h>
using namespace std;
#define pi = 3.14159265358979323846
#define int long long
typedef pair<int,int> pii ;
const int N = 1919810;
int a[N],b[N];
vector<pii>vis(N);
void solve()
{
    int n;
    cin >> n;
    vector<pii> ans;
    for(int i=1;i<=n;i++){
        cin >> a[i];
        vis[a[i]].first = i;
    }
    for(int i=1;i<=n;i++){
        cin >> b[i];
        vis[b[i]].second = i;
    }
    int flag = 1;
    for(int i=n;i>=1;i--){
        while(vis[i].first > vis[i].second){
            int id = vis[i].first - 1;
            while(id >= 1 && (vis[a[id]].second < vis[i].first || a[id] < i)){
                id-- ;
            }
            if(id < 1) break;
            ans.push_back({id,vis[i].first});
            a[vis[i].first] = a[id];
            vis[a[id]].first = vis[i].first;
            vis[i].first = id;
            a[id] = i;
        }
        if(vis[i].first > vis[i].second){
            flag = 0;
            break;
        }
    }
    if(flag == 0){
        cout << -1 << "\n";
        return ;
    }
    cout << ans.size() << "\n";
    for(int i=0;i<=ans.size()-1;i++){
        cout << ans[i].first << " " << ans[i].second << "\n";
    }
}

signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int t = 1;
    cin >> t;
    while (t--)
    {
        solve();
    }
}