The 6 kg block is then released and accelerates
to the right, toward the 2 kg block. the
surface is rough and the coefficient of friction
between each block and the surface is 0.3 . the
two blocks collide, stick together, and move
to the right. remember that the spring is not
attached to the 6 kg block.
find the speed of the 6 kg block just before
it collides with the 2 kg block.
answer in units of m/s

5.709 m/s

Explanation:

Assuming compression of spring as 0.6m and spring constant of 602 N/m

The initial energy stored in the spring will be given by

By substitution, the initial energy is \

Kinetic energy of the 6 Kg block is given by subtracting energy lost due to friction from the initial stored energy hence

where m is mass, v is speed, g is acceleration due to gravity, x is the spring compression and is the coefficient of friction

Making v the subject then  

i think the answer is a, hope this is right, that would be my best guess.