#include<bits/stdc++.h>
using namespace std;
#define fastIO ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define int long long int
#define fi first
#define se second
#define pub push_back
#define veci vector<int>
#define pi pair<int,int>
#define all(v) (v).begin(), (v).end()
#define rep(i, l, r) for(int i=(int)(l);i<(int)(r);i++)
#define repi(i, l, r) for(int i=(int)(l);i<(int)(r);i+=2)
#define repd(i, l, r) for (int i=(int)(l);i>=(int)(r);i--)
#define clrg(i, l, r) for(int i=(int)(l);i<(int)(r);i++)vis[i]=0,v[i].clear();
int power(int x, unsigned int y){int res = 1;while (y > 0){ if (y & 1){res = res*x;} y = y>>1;x = x*x;}return res;}
int powermod(int x, unsigned int y, int p){int res = 1;x = x % p;while (y > 0){if (y & 1){res = (res*x) % p;}y = y>>1; x = (x*x) % p;}return res;}
#define print2d(mat,n,m){for(int i=0;i<(int)(n);i++){for(int j=0;j<(m);j++){cout<<mat[i][j]<<" ";}cout<< endl;}}
#define clr(a,x) memset(a,x,sizeof(a))
#define rr(v) for(auto &val:v)
#define print(v) for (const auto itr : v){cout<<itr<<' ';}cout<<"\n";
#define ln length()
#define sz size()
#define mod 1000000007
#define elif else if
int32_t main(){
   fastIO
   int t;
   cin>>t;
   while(t--)
   {
      int n,as=0,bs=0,ans=0;
      cin>>n;
      veci a(n),b(n);
      rep(i,0,n)
         cin>>a[i];
      rep(i,0,n)
         cin>>b[i];
      as=accumulate(a.begin(),a.end(),0);
      bs=accumulate(b.begin(),b.end(),0);
      if(as!=bs)
      {
         cout<<"-1\n";
         continue;
      }
      else
      {
         rep(i,0,n)
            if(a[i]>b[i])
               ans+=a[i]-b[i];
         cout<<ans<<endl;
         rep(i,0,n)
         {
            if(a[i]>b[i])
            {
               rep(j,0,n)
               {
                  if(i!=j && a[j]<b[j])
                  {
                     int tem=min(a[i]-b[i],b[j]-a[j]);
                     rep(k,0,tem)
                     {
                        a[i]--;a[j]++;
                        cout<<i+1<<" "<<j+1<<endl;
                     }
                  }
               }
            }
         }
      }
   }
   return 0;
}