Easy, just do 60 seconds which equals a minute. Since we know that now simply use 60 minutes to get you to an hour. If your doing minutes to hours make sure there is a 0 at the end.
21/25
Change to decimal:-
Divide numerator by denominator.
21/25
21 ÷ 25 = 0.84
21/25 = 0.84
Change to a percentage:-
0.84 × 100 = 84
21/25 = 0.84 = 84%
If you add a zero at the end it is easier to understand. 0.20 > 0.18 because 20 is greater than 18