Let Y be the Yaw age. Then from the condition, Kwasi's age is (47 + 4 + 4 - Y) = 55 - Y. From the condition, you have this proportion = . Hence, 9*(55 - Y) = 2Y 9*55- 9Y = 2Y 9*55 = 2Y + 9Y = 11Y. Hence, Y = = 9*5 = 45 is the Yaw's age now.