You're looking for the whole.
So, you set it up 48/x = 75/100
Then you cross multiple 100x48 which is 4,800
Then you have 4,800 = 75x
You then have to divide 75/75 to get x alone, and what is done on one side has to be done to the next, so you then get 4,800/75
Giving you an answer of x = 64
Hope this helped (;
