Couldn't figure this one out for the life of me... got a few steps down and then it all went downhill from there.

If the concentration of a drug in the bloodstream at time "t" is given by this function,

where a, b(b>a), and k are positive constants that depend on the drug, at what time is the concentration at its highest level?

And the second question:

The motion of a particle is given by s(t) = 5cos(2t + pi/4). What are the maximum values of the displacement, the velocity, and the acceleration?