Don't know where ya went....
derivative of the velocity function is the acceleration function....you got that !
derivative of the velocity function also shows the slope of the velocity function at each point
where the slope goes from positive to negative or from negative to positive
the acceleation is too....these are the points where velocity will be a maximum (maybe negative or maybe positive value)
these occur where the acceleration function = 0 (slope = 0 as it goes from pos to neg or neg to pos)
the derivative of the given velocity funtion is given as -10(s^2-4s-4) / (s+4)^2
-10(s^2-4s-4)/(s+4)^2 = 0
-10s^2 +40s+40 = 0 Use Quadratic Formula
s = 2+- 2 sqrt2 these are the points where accel = 0
Plug these values into the orignal Velocity equation to calculate the values......pick the one that is maximum (here I do not know if they want most positive or greatest magnitude)
Use s =3 in the derived ACCELERATION equation to calculate the acceleration at s = 3
The graph above should help to verify your answers......