Two blocks of masses M and 3M are placed on a horizontal, frictionless surface. A light spring is attached to one of them, and the blocks are pushed together with the spring among them, as seen in the figure below. A cord initially holding the blocks together is burned; after this the block of mass 3Mmoves to the right with a speed of v1=2.06 m/s. Compute the original elastic energy in the spring if M = 0.300 kg.