又见GCD：

#include
     
      using namespace std;int gcd(int a,int b){    while(a%b)    {        int r=a%b;        a=b;        b=r;    }    return b;}int main(){    int n,a,b,c,i,j;    cin>>n;    for (i=0;i
      
       >a>>b;        c=2*b;        while(gcd(a,c)!=b)        {            c+=b;        }        cout<
       
        <