The block shown are released from rest with the spring unscratched. The pulley and the horizontal surface

Question:

The block shown are released from rest with the spring unscratched. The pulley and the horizontal surface are frictionless, the spring constant k = 500 N/m, and the two blocks have equal masses of m = 8 kg each. After the system in released, what is the maximum extension (m m) of the spring?