=- 1/5x

(2)9ab^2+6abc / 3a^2b

=3ab(3b+2c)/3a？ b

=(3b+2c)/a

(3)9a^2+6ab+b^2 / 3a+b

=(3a+b)？ /(3a+b)

=3a+b

(4)x^2-36 / 2x+ 12

=(x+6)(x-6)/2(x+6)

=(x-6)/2