A 0.40 kg mass vibrates at the end of a horizontal spring (k=0.900 N/m) along a frictionless surface. The kinetic energy at the equilibrium position is 6.00 x 10^-3 J

a) What is the speed of the object at the equilibrium position?

b) The formula for elastic potential energy is Ep=0.5 kx^2 (k = spring constant, x = displacement) What is the maximum displacement

c) what is the total mechanical energy when the mass is halfway between the end position and the equilibrium position?

For a) I got 0.173 m/s for b) x = 0.11547 m c) I have no clue