Hey i think u forgot to insert the picture of the triangle lol
To transform it into percent we want to have 100 into denominator. The easiest way is divide numerator and denominator by 3 (thats because than it doesnt change the value of fraction), so:

- its the result
300miles/20sec=?miles/1min
900miles/60sec=?miles/1min
900miles/1min=?miles/min
?=900 miles