A bullet is fired through a board, 14.0 cm thick, with its line of motion perpendicular to the face of the board. If it enters with a speed of 450 m/s and emerges with a speed of 220 m/s, what is the bullet's acceleration as it passes through the board?

a.-500km/s2/2

b.-550 km/s2/2

c.-520 km/s2/2

d.-275 km/s2/2

e.-360 km/s2