Question 785698
3(x + 2y) = 3(9)

  3x + 6y = 27 subtract the other equation from this one.
-(3x - y = -15)
 7y = 42
7y/7 = 42/7
y = 6

x + 2(6) = 9
x + 12 = 9
x = 9 -12 
x = -3

check:
3(-3) - 6 = -15
-9 -6 = -15
-15 = -15

-3 + 2(6) = 9
-3 + 12 = 9
9 = 9