If 3x =15 and x+y =7 what is (3y)^2?

First divide 15 by 3 to find xx= 15/3 = 5Now use x to find yx +y = 7 substitue x. 5+y=7y= 7-5= 2Now you know x=5 and y=2 use this to calculate the answer, remembering to do the sum within the brackets first.(3y)^2 = (3x2)^2 = 6^2 = 36