#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
inline int read(){
	char c=getchar();
	int f=1,x=0;
	for(;c<'0'||c>'9';c=getchar()) if(c=='-') f=-1;
	for(;c>='0'&&c<='9';c=getchar()) x=x*10+c-'0';
	return f*x;
}
void solve();
int main(){
	cin.tie(0)->sync_with_stdio(false);
	int t=1;
	cin>>t;
	while(t--)solve();
	return 0;
}

const int N=3000;
int a[N],b[N],ia[N],ib[N];
void solve(){
	int n;cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a[i];
		ia[a[i]]=i;
	}
	for(int i=1;i<=n;i++){
		cin>>b[i];
		ib[b[i]]=i;
	}
	
	set<int>s1,s2;
	
	s1.insert(ia[n]);
	s2.insert(ib[n]);
	
	
	vector<pair<int,int>>V;
	for(int i=n-1;i;i--){
		
		
		vector<int>S1,S2;
		for(auto w:s1)S1.push_back(w);
		for(auto w:s2)S2.push_back(w);
		
		for(int i=0;i<S1.size();i++)if(S1[i]>S2[i]){
			cout<<-1<<endl;
			return;
		}
		
		int p=lower_bound(S1.begin(),S1.end(),ia[i])-S1.begin();
		int q=lower_bound(S2.begin(),S2.end(),ib[i])-S2.begin();
		
		
		if(q<p){
			V.emplace_back(ib[i],S2[q]);
			for(int j=q;j<p-1;j++)V.emplace_back(S2[j],S2[j+1]);
		}
		else if(q>p){
			V.emplace_back(S2[q-1],ib[i]);
			for(int j=q-1;j>p;j--)V.emplace_back(S2[j],S2[j-1]);
		}
		
		s1.insert(ia[i]);
		s2.insert(ib[i]);
	}
	
	cout<<V.size()<<endl;
	
	for(auto i=V.rbegin();i!=V.rend();i++){
		cout<<(i->first)<<" "<<(i->second)<<endl;
	}
	
}