Question

A horizontal spring with force constant k = 685 N/m is attached to a wall at one end and to a block of mass m = 2.50 kg at the other end that rests on a horizontal surface. The block is released from rest from a position 3.70 cm beyond the spring's equilibrium position.
(a) If the surface is frictionless, what is the speed of the block as it passes through the equilibrium position?
I already know that a is 0.612 m/s.
(b)If the surface is rough and the coefficient of kinetic friction between the box and the surface is 𝜇k = 0.200, what is the speed of the block as it passes through the equilibrium position?

I just need to find b.