could u help me with these?

James blowing machine blows spherical bubbles whose surface area ,S, increases at the rate of 25cm^2/s. What is the rate the of increase of the radius,r, when the radius is 5cm?

I ended up with 0.199cm/s

and...

find maximum,minimum or point of inflection

f(x)=x^3-3x+2

give the values of x which are concave down

i got (-1,4) as maximum and (1,0) as minimum unsure about concave bit =S

is this correct?

2)3sqrr(2x-1)

2/3(2x-1)^2/3

thanks in advance