/******************************
 *                            *
 *    author :  rion_cse      *
 *    created:  11.07.2021    *
 *                            *
 ******************************/
 
/*******************************************************
 *                                                     *
 *  ***-->    BISMILLAHIR RAHMANIR RAHIM    <--***     *
 *  ***--> ISLAMIC UNIVERSITY OF BANGLADESH <--***     *
 *  ***--> COMPUTER SCIENCE AND ENGINEERING <--***     *
 *                                                     *
 *******************************************************/
 
#include<bits/stdc++.h>
const int MOD=1e9+7;
 
#define  pf                 printf
#define  sc                 scanf
 
#define  s1(n)              scanf("%d",&n)
#define  s2(n1,n2)          scanf("%d %d",&n1,&n2)
#define  s3(n1,n2,n3)       scanf("%d %d %d",&n1,&n2,&n3)
#define  s4(n1,n2,n3,n4)    scanf("%d %d %d %d",&n1,&n2,&n3,&n4)
 
#define  ss1(n)             scanf("%lld",&n)
#define  ss2(n1,n2)         scanf("%lld %lld",&n1,&n2)
#define  ss3(n1,n2,n3)      scanf("%lld %lld %lld",&n1,&n2,&n3)
#define  ss4(n1,n2,n3,n4)   scanf("%lld %lld %lld %lld",&n1,&n2,&n3,&n4)
 
#define  p1(x)              printf("%I64d",x)
#define  p2(x,y)            printf("%I64d %I64d",x,y)
#define  p3(x,y,z)          printf("%I64d %I64d %I64d",x,y,z)
 
#define  fi(i,a,b)          for(long long i=a;i<=b;i++)
#define  fm(i , a)          for(long long i=1;i<=a;i++)
#define  fd(i,a,b)          for(long long i=b;i>=a;i--)
 
#define  clr(x)             memset(x,0,sizeof(x))
#define  cln(x)             memset(x,-1,sizeof(x))
 
#define  fw                 freopen("output.txt","w",stdout);
 
typedef long long int ll;
///ll ar[1009],arr[1009];
using namespace std;
 
/*ll LCM(ll a,ll b)
{
    return (a/(__gcd(a,b)))*b;
}*/
 
int main()
{
     ll t;
     cin>>t;
     while(t--)
     {
      ll n,i,j;
      cin>>n;
      ll ar[n+5],br[n+5],s=0,s1=0;
      vector< ll > v,vc;
      for(i=1;i<=n;i++)
      {
       cin>>ar[i];
       s+=ar[i];
      }

      for(i=1;i<=n;i++)
      {
        cin>>br[i]; 
        s1+=br[i];
      }
      
      if(s!=s1) cout<<"-1"<<endl;
      else {
             for(i=1;i<=n;i++)
             {
              if(ar[i]>br[i]){
                for(j=1;j<=(ar[i]-br[i]);j++)
                v.push_back(i);
              }

              else if(ar[i]<br[i]){
                 for(j=1;j<=(br[i]-ar[i]);j++)
                vc.push_back(i);
              }
             }
             cout<<v.size()<<endl;
             for(i=0;i<v.size();i++)
              cout<<v[i]<<" "<<vc[i]<<endl;
           }
   }
    return 0;
}
