#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
const int N = 100010;
typedef long long ll;
typedef pair<int, int> pii;
std::mt19937 rng {std::chrono::steady_clock::now().time_since_epoch().count()};

template <typename T>
void debug(T x) {
    cerr << x << '\n';
}

template <typename T, typename... Args>
void debug(T x, Args... args) {
    cerr << x << ' ';
    debug(args...);
}

void solve() {
    int n;
    cin >> n;
    vector<int> a(n + 1), b(n + 1);
    map<int, int> idx_a, idx_b;
    for (int i = 1; i <= n; i ++ ) {
        cin >> a[i];
        idx_a[a[i]] = i;
    }
    for (int i = 1; i <= n; i ++ ) {
        cin >> b[i];
        idx_b[b[i]] = i;
    }
    int now = n;
    bool ok = 0;
    vector<pii> ans;
    while (now) {
        if (idx_a[now] == idx_b[now]) {
            now --;
            continue;
        } else if (idx_a[now] > idx_b[now]) {
            ok = 1;
            break;
        } else {
            ans.push_back({idx_a[now], idx_b[now]});
            swap(a[idx_a[now]], a[idx_b[now]]);
            swap(idx_a[a[idx_a[now]]], idx_a[a[idx_b[now]]]);
            now --;
        }
    }
    if (ok) {
        cout << -1 << '\n';
    } else {
        cout << ans.size() << '\n';
        for (auto [x, y] : ans) {
            cout << x << ' ' << y << '\n';
        }
    }
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int T = 1;
    cin >> T;
    while (T -- ) {
        solve();
    }
    return 0;
}