If Jack walked 8 miles in 1 hour and 15 minutes, what was his rate of walking in miles per hour?  Choose the correct answer
A) 4 B) 4.5 C) 6 D) 6.4 E) 15

Rationale: "distance walked in 1 hour and 15 mins = 8 miles speed per hour = distance / time = 8 / ( 5 / 4 ) = 6.4 miles per hour answer d"
Answer: D