Two blocks of masses `m_(1)= 2 kg` and `m_(2) = 4 kg` are moving in the same direction with speeds `v_(1) = 6 m//s` and `v_(2) = 3 m//s`, respectively on a frictionless surface as shown in the figure. An ideal spring with spring constant `k = 30000 N//m` is attached to the back side of `m_(2)`. Then the maximum compression of the spring after collision will be