Explanation:
300/20 × 3/3 = 900/60
* 60 sec is 1 min therefore you want to get 60 secs in the denominator. In order to get that, you need to multiply.
900/60 divided by 60/60 is 15/1.
So 300m/20sec = 900m/60sec = 900mpm
If we're to do the same for all then it would be:
30m/20sec = 90m/60sec = 90mpm
15m/20sec = 45m/60sec = 45mpm
3m/20sec = 9m/60sec = 9mpm