-w^2(w-15)
-w2 is -(w2) not (-w)2 because exponentiation (raising to a power) normally takes priority over the unary minus.
This would mean -w2(w - 15) = w2(-w + 15) = -w3 + 15w
To ensure there is no confusion you could use brackets!
-w^2*(w-15)
=-w*-w*(w-15)
=-w*-w^2+15w
=w^3+15w
=w(w^2+15)
Most simplified form
