Answer:
(a)
(b)
Step-by-step explanation:
Given the expression: 
<u>Part A</u>
If we consider the terms:
in the expression. The common terms are 3 and y.
Therefore the greatest common factor of the terms is 3y.
Factoring this out, we obtain:

<u>Part B</u>
Next, we factor the expression completely
![3x^3y + 12xy - 9x^2y -36y\\=3y(x^3+4x-3x^2-12)\\$Rearranging we obtain:\\=3y(x^3-3x^2+4x-12)\\=3y[x^2(x-3)+4(x-3)]\\=3y(x^2+4)(x-3)](https://tex.z-dn.net/?f=3x%5E3y%20%2B%2012xy%20-%209x%5E2y%20-36y%5C%5C%3D3y%28x%5E3%2B4x-3x%5E2-12%29%5C%5C%24Rearranging%20we%20obtain%3A%5C%5C%3D3y%28x%5E3-3x%5E2%2B4x-12%29%5C%5C%3D3y%5Bx%5E2%28x-3%29%2B4%28x-3%29%5D%5C%5C%3D3y%28x%5E2%2B4%29%28x-3%29)