This is the the concept of algebra:
The total amount of hours spent on physical class is 7/8 hours.
an hour has 60 min, then the total number of minutes spent in this class will be:
7/8×60=52.5 minutes
a] Total number of minutes that is spent on warming up and cooling down will be given by:
(Total time the lesson takes)×(fraction of time spent on warming up and cooling down)
=3/10×52.5
=15.75 minutes
b] Total number of minutes that aren't spent on instructions will be given by the total number of minutes the lesson takes minus total number of minutes instructions takes. This can be shown as follows:
Total number of minutes the lesson takes=52.5 min
Total number of minutes instruction takes=1/5×52.5=10.5 min
thus the total number of time that is not spent on instructions will be:
52.5-10.5=42 minutes.
