Turn the fractions into decimals by dividing the top number by the bottom number, then multiply that by 100 to make it a percentage:
34/40 = 0.85 x 100 = 85%
20/25 = 0.80 x 100 = 80%
53/60 = 0.883 x 100 = 88.3%
The Last one is the highest percentage, so 53/60 is the best score.
