Please help me with this. Two blocks A and B of masses m and 2m respectively are connected by a spring of force constant k. The masses are moving to the right with uniform velocity v = 10m/s each, the heavier mass leading the lighter one. The spring in between them is of natural length during the motion. Block B collides with a third block C of mass m, at rest. The collision being completely inelastic. Find minimum speed (in m/s) of block A in the subsequent motion.

options:
(A) 5 (B) 6 (C) 8 (D) 10​