Sam drove 96 miles in 90 minutes. His average speed during the first 30 minutes was 60 \mathrm{mph} (miles per hour), and his average speed during the second 30 minutes was 65 \mathrm{mph}. What was his average speed, in mph, during the last 30 minutes?
Answer Choices
A. 64
B. 65
C. 66
D. 67
E. 68