(9ab^2+6abc)/3a^2b
=3ab(3b+2c)/3a^2b
=(3b+2c)/a
(9a^2+6ab+b^2)/(3a+b)
=(3a+b)^2/(3a+b)
=3a+b
(x^2-36)/(2x+12)
=(x+6)(x-6)/2(x+6)
=(x-6)/2