The each class is 64 minutes or 1 hour 4 minutes long.
Step-by-step explanation:
1 hour = 60 minutes.
Time spent in 6 classes :
Time spent in 6 classes = Total time - (lunch period + switching classes)
⇒ 456 - (30+42)
⇒ 456 - 72
⇒ 384 minutes.
The Time for each of 6 classes :
Time for each class = Time spent for all 6 classes / 6
⇒ 384/6
⇒ 64 minutes.
⇒ 1 hour 4 minutes.