Here is my friendly solution i'll skip the proof part for now. I am working on the others.
To calculate this we should firstly calculate that how many laps can he do in an hour. So assuming that he does all the laps at the same rate he must do 120 laps in an hour.
Now because he burns 1200 calories per hour we can see how many number of hours it would take him to burn 15000 calories. So it would take him around 15000 / 1200 = 12.5 hours. So now we will multiply 12.5 by 120 laps as that is the number laps he can do in an hour. So that is around 1500 laps a day.
Answer:= 261.905% increase
Solution:
Calculate percentage change
from V1 = 21 to V2 = 76
(V2−V1)|V1|×100
(V2−V1)|V1|×100
=(76−21)|21|×100
=(76−21)|21|×100
=5521×100
=5521×100
=2.61905×100
=2.61905×100
=261.905%change
=261.905%change
=261.905%increase
