Your answer would be 3/4 = 15/20 = 75/100
Now their are two ways to figure out this problem.
You can look at the relationship with 3 and 15. 3 x 5 is 15 so you can determine that something x 5 equals 20. Well 20 x 5 = 4 so your answer is 3/4.
You would then do the same thing with 15/20.
20 x 5= 100, so do 15 x 5 which is 75. Answer is 75/100
Now here is the 2nd way you could have done it.
well we know that 3/4 equals .75 and that equals 75/100 as a fraction. Then divide top and bottom by 5 to get 15/20.