Application of derivative

Hi guys, i have got a few question that needs help before my exams next week :(

The surface area of a cube with side x cm, is increasing at a rate of 16cm2/s

Whnt the total surface area of the cube reaches 216cm2

a)show that the volume of the cube is 216cm3

b) find the rate which its volume is increasing

I completed part a) but for part b, they wants dv/dt so i figure out since da/dt is given i need to find dv/da. But I am stuck ! anyone could explain to me ? THANKS IN ADVANCE ! :D

Re: Application of derivative

Let be the surface area and be the side of the cube.

You have .

So .

Taking , .

Re: Application of derivative