Aball rolls down a ramp for 15 seconds. if the initial velocity of the ball was 0.8m/s and the final velocity was 7 m/sec, what was the acceleration of the ball?

A ball rolls down a ramp for 15 seconds. If the initial velocity of the ball was .08m/sec and the final velocity was 7m/sec, what was the acceleration of the ball?
F:
D:
Ans:

F:a=vf-vi/t
D:a=?
vi=0.8 m/s
vf=7m/s
t=15sec
Ans: .41m/s
a=vf-vi/t
a=1800-1000/.03
a=.41

The low lands i believe