D. 1 hr 12 min
Feedback New speed =6/7 of usual speed
Speed and time are inversely proportional.
Hence new time =7/6 of usual time
Hence, 7/6 of usual time - usual time =12 minutes
⇒1/6 of usual time =12 minutes
Therefore, usual time =12×6=72 minutes=1 hour 12 minutes