Simplify 2^9/2^6

A. 2^15

B. 4^3

C. 4^-3

D. 2^3

Martha is training for a duathlon, which includes biking and running. she knows that yesterday she covered a total distance of over 55.5 miles in more than than 4.5 hours of training. martha runs at a speed of 6 mph and bikes at a rate of 15.5 mph.