When Sam is 13 his mother will be 39 which is 3 times as old as he is. So Sam's mother will be 3 times as old as Sam will be in 11 years. (Your answer is 11 years.)
You set the corresponding sides equal to each other and solve for x as you would in a normal equation
You cant solve but u can simplify which would be 2b=14
11 - (-5) = 16. Hope that helped!
