A 0.6 kg tennis ball, initially moving at 12 m/s, is struck by a racket causing it to rebound in the opposite direction at a speed of 18 m/s. A high speed movie film determines that the ball and the racket are in contact for 0.05 s. What average net force is exerted on the ball by the racket?
A. 36 N
B. 48 N
C. 60 N
D. 72 N