+108 Hello!
So when we distribute all the variables in (Ax+1)(Bx+5), we get ABx^2+5Ax+Bx+5. Therefore, AB has to equal 6, and 5A+B has to equal 17. So the answer is 6, and we can check this by finding the values of A and B. These come out to be 3 for A and 2 for B. Hope this helped!
