This is the problem I am having...

All edges of a cube are expanding at a rate of 3 centimeters per second. How fast is the volume changing when each edge is

(a) 1 centimeter
(b) 30 centimeters


The equation I am using is

V = S


This is what I did

dv/dt = 3s ds/dt
dv/dt = 3 (1) x 3
dv/dt = 3 x 3
dv/dt = 9

dv/dt = 3s ds/dt
dv/dt = 3 (30) x 3
dv/dt = 3 (900) x 3
dv/dt = 2700 x 3
dv/dt = 8100

I am just wondering wheter or not I did this equation right so I can look back over it and find the mistake.