How do I factorise 3y+9z+by+3bz?
Just explain to me what you would do to factorise it.
Hint: Try looking for common factors one at a time.
For example if you factorize by y you get 3y + by = y(3+b). Factorize by z you get 3bz + 9z = z(3b+9).
Try doing this for different terms and see what you get.
Also note that ab + ac = a*(b+c).