MATH!!!!!!!!代數

1)
a + b(3+a) = 27
a + 3b + ab = 27......(1)
b*4 + a(2+b) = 36
2a + 4b + ab = 36.....(2)
(2) - (1) :
a + b = 9
a = (9-b),sub to (1):
(9 - b) + 3b + b(9 - b) = 27
9 + 2b + 9b - b^2 = 27
b^2 - 11b + 18 = 0
(b - 2)(b - 9) = 0
b = 2 or b = 9
so a + 2 = 9 or a + 9 = 9
a = 7 or a = 0
So when a = 7 , b = 2
when a = 0 , b = 9