5. Two blocks of masses m and 2m are held against a massless compressed spring within a box of mass 3m and length 4L whose center is at x=0. All surfaces are frictionless. After the blocks are released, they are each at a distance L from the ends of the box when they lose contact with the spring. Both blocks keeps moving until they collide with the box and stick to it. Find the distance of the center of the box moves from x=0 after both blocks stick to the box.