Problem $4(10$ points$)$: A a powerful spring$-$loaded projectile launcher is compressed a distance of $0\mathrm{.}18$ meters and then fires a $0\mathrm{.}06$ kg steel ball. This ball then embeds itself in a $0\mathrm{.}9$ kg block of wood which was initially at rest. Immediately after the collision, the ball$/$block together have a speed of $2\mathrm{.}8\frac{m}{s}.$

A$)$ What was the speed of the steel ball right before the collision?

B$)$ What was the spring constant of the launcher?