I'm having trouble with part e)

Two blocks of masses m and 3m are placed on a frictionless, horizontal surface. A light spring is attached to the more massive black, and the blocks are pushed together with the spring between them as shown in the figure below. A cord initially holding the blocks together is burned; after that happens, the block of mass 3m moves to the right with a speed of 33m = 2.30 m/s. (a) What is the velocity of the block of mass m? (Assume right is positive and left is negative.) -6.9 y m/s (b) Find the system's original elastic potential energy, taking in = 0.370 kg. 11,74 J (c) Is the original energy in the spring or in the cord? (Q in the spring in the cord (d) Is the momentum of the system conserved in the bursting-apart process? Yes No V (e) If the spring was compressed by 4.50 cm, what is the spring constant of the spring? N/m