Spring and Work Question

A block of mass m=2 kg, attached to a spring of stiffness k=30 N/m, is lying on a horizontal desk.
Initially, the spring is suppressed by A=10cm. When it is released, the block pushed by the spring
passes through the equilibrium position and extends the spring by 5 cm. What is the friction
coefficient between the block and the desk?

Have an exam in the morning so hopefully someone can explain this! (answer is 0.04)

let u be the friction coefficient between the block and the desk

stored energy in spring
= 0.5 * 30 * 0.1 ^2
= 0.15

stored energy after equilibrium position
= 0.5 *30 * 0.05^2
= 0.0375

friction force = u * 2g
work done by friction force
= u * 2g * 0.15

0.15 = 0.0375 + u * 2g * 0.15

u = 0.0382 ---answer