You can put this solution on YOUR website! If we multiply B2*7B, our first step would be to multiply the last digit in 7B and the last digit in B2 to get 2*B. Since B is a single digit, we know that 2*B is going to be at most 18 (since 9 is the largest that B can be and 2*9=18). So if we subtract 10 off 2*B the largest that 2*B-10 is now 8 (which means that we now can say that 2*B-10 is equal to a single digit).