How to solve this:

6 a Calculate the displacement in terms of x0, expressed as a fraction of the amplitude x0, of a particle moving in simple harmonic motion with a speed equal to half the maximum value.

b Calculate the displacement at which the energy of the particle has equal amounts of kinetic and of potential energy

I am stuck at both (a) and (b) and just don't know how to do this. Thanks for your help in advance!.