I'm having trouble with this physics problem:

A bullet traveling horizontally with a velocity of magnitude 400 m/s, is fired into wooden block with mass 0.800 kg initially at rest on a level surface. The bullet passes through the block and emerges with its speed reduced to 120 m/s. the block slides a distance of 45 cm along the surface from its initial position. A) what is the coefficient of kinetic

friction between the block and surface? B) what is the decrease in

kinetic energy of the bullet? C) what is the kinetic energy of the block at the instant after the bullet passes through it?

i started doing part A, and found that the velocity while the bullet is in the block is 1.99 m/s. i also assumed that the

work done by friction was equal to the change in kinetic energy of the system. but when i used this information to solve for the coefficient of friction i got something way too high. the answers are supposed to be : A) 0.222, B)-291J, C)0.784 J, but i have no idea of how to set this problem up. Please Help!!!