Blocks A (mass 3.50 kg) and B (mass 8.50 kg) move on a frictionless, horizontal surface. Initially, block B is at rest and block A is moving toward it at 4.00 m/s. The blocks are equipped with ideal spring bumpers. The collision is head-on, so all motion before and after the collision is along a straight line. Let x be the direction of the initial motion of block A. Find the maximum energy stored in the spring bumpers.