Blocks $A($mass $2\mathrm{.}00$ kg $)$ and $B($mass $8\mathrm{.}50$ kg $)$ move on a frictionless, horizontal surface. Initially, block $B$ is at rest and block $A$ is moving toward it at $5\mathrm{.}00\frac{m}{s}.$ 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 $A.$