You have been asked to design a "ballistic spring system" to measure the speed of bullets. A bullet of mass is fired into a block of mass . The block, with the embedded bullet, then slides across a frictionless table and collides with a horizontal spring whose spring constant is . The opposite end of the spring is anchored to a wall. The spring's maximum compression is measured. Find an expression for the bullet's initial speed in terms of M, m, k and d.