/*??
 ?2??????????
 ????
 ?1?????????n????????2???1?????a??2????b(a > b)??????????????????????100?
 ????
 n????????????????????
 ????
 2
 
 9999999999999999999999999999999999999
 
 9999999999999
 
 
 
 5409656775097850895687056798068970934546546575676768678435435345
 
 1
 ????
 9999999999999999999999990000000000000
 
 5409656775097850895687056798068970934546546575676768678435435344
 */
char imim[101],isub[101],istore[101];
int carry=0;
char *p=NULL,*q=NULL;
void subtraction()
{
    if(q==isub)
    {
        *p=(*p-*q-carry+'0');
    }
    else
    {
        if(*p>=(*q+carry))
        {
            
            *p=(*p-*q-carry+'0');
            carry=0;
        }
        else
        {
            *p=(*p+10-*q-carry+'0');
            carry=1;
        }
        p--;q--;
        subtraction();
    }
}
int main()
{
    int n=0;
    cin>>n;
    for(int i=0;i<n;i++)
    {
        memset(imim,'0',sizeof(imim));
        memset(isub,'0',sizeof(isub));
        memset(istore,'0',sizeof(istore));
        carry=0;
        cin>>imim>>istore;
        int gap=0;
        gap=strlen(imim)-strlen(istore);
        for(int i=0;i<=strlen(istore);i++)
        {
            isub[i+gap]=istore[i];
        }
        p=imim+strlen(imim)-1;
        q=isub+strlen(isub)-1;
        subtraction();
        cout<<imim<<endl;
    }
    return 0;
}

