//Author: Kevin
#include<bits/stdc++.h>
//#pragma GCC optimize("O2")
using namespace std;
#define ll long long
#define ull unsigned ll
#define pb emplace_back
#define mp make_pair
#define ALL(x) (x).begin(),(x).end()
#define rALL(x) (x).rbegin(),(x).rend()
#define srt(x) sort(ALL(x))
#define rev(x) reverse(ALL(x))
#define rsrt(x) sort(rALL(x))
#define sz(x) (int)(x.size())
#define inf 0x3f3f3f3f
#define pii pair<int,int>
#define lb(v,x) (int)(lower_bound(ALL(v),x)-v.begin())
#define ub(v,x) (int)(upper_bound(ALL(v),x)-v.begin())
#define uni(v) v.resize(unique(ALL(v))-v.begin())
#define longer __int128_t
void die(string S){puts(S.c_str());exit(0);}
int a[3030],b[3030],n;
int mn[3030<<2];
void modify(int x,int l,int r,int p,int v)
{
	if(l==r)
	{
		mn[x]=v;
		return ;
	}
	int mid=(l+r)/2;
	if(p<=mid)
		modify(x<<1,l,mid,p,v);
	else
		modify((x<<1)|1,mid+1,r,p,v);
	mn[x]=min(mn[x<<1],mn[(x<<1)|1]);
}
int query(int x,int l,int r,int ql,int qr)
{
	if(l==ql&&r==qr) return mn[x];
	int mid=(l+r)/2;
	if(qr<=mid)
		return query(x<<1,l,mid,ql,qr);
	if(ql>mid)
		return query((x<<1)|1,mid+1,r,ql,qr);
	return min(query(x<<1,l,mid,ql,mid),query((x<<1)|1,mid+1,r,mid+1,qr));
}
int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	int t;
	cin>>t;
	while(t--)
	{
		cin>>n;
		for(int i=1;i<=n;i++)
		{
			cin>>a[i];
			modify(1,1,n,a[i],i);
		}
		for(int i=1;i<=n;i++)
			cin>>b[i];
		bool ok=true;
		vector<pii> res;
		int p=1;
		while(p<=n)
		{
			if(a[p]==b[p])
			{
				modify(1,1,n,a[p],inf);
				p++;
				continue;
			}
			if(a[p]<b[p])
			{
				ok=false;
				break;
			}
			int x=query(1,1,n,b[p],a[p]-1);
			swap(a[p],a[x]);
			modify(1,1,n,a[p],p);
			modify(1,1,n,a[x],x);
			res.pb(p,x);
		}
		if(!ok)
			cout<<"-1\n";
		else
		{
			cout<<sz(res)<<'\n';
			for(auto pr:res)
				cout<<pr.first<<" "<<pr.second<<'\n';
		}
	}
	return 0;
}