A horizontal spring with spring constant $85$ N$/$mN$/$m extends outward from a wall just above floor level. A $5\mathrm{.}5$ kgkg box sliding across a frictionless floor hits the end of the spring and compresses it $3\mathrm{.}5$ cmcm before the spring expands and shoots the box back out. How fast was the box going when it hit the spring? How fast was the box going when it hit the spring?