..Help would be greatly appreciated....

The volume of a rectangular prism cereal box

is modelled byV = 20x^2 + 500x + 3000.

(a)Factorise this fully. Mr F says: V = 20(x^2 + 25x + 150) = 20(x + 10)(x + 15).

(b)What are the dimensions of the box? Mr F says: Obviously, although you don't state this, the dimensions depend on x. So solve V = 0 for x.

(c)What is the volume of the box if one side is 15 cm? Mr F says: Answers to (a) and (b) should give you (c).

Cheers