A ball rolling down an incline travels 6.0 cm in the first 0.25

A ball rolling down an incline travels 6.0 cm in the first 0.25 seconds, and 24 cm in the first 0.50 seconds. Find: 

1. a)  The average speed for the first quarter second time interval 

2. b)  The average speed for the second quarter second time interval. 

3. c)  Find its acceleration.