X = 21
Y = 30
X:
(3x - 15) + (6x + 6) = 180 -- combine like terms
9x - 9 = 180 -- add 9 to both sides
9x = 189
x = 21
Y:
Plug x into 3x-15
3(21) - 15 = y + 18
63 - 15 = y + 18
48 = y + 18 -- subtract 18 from both sides
y = 30
