3/4 of what equals 75

100 
75 times 1.333333333333333 equals 100

So, you need to know your vocabulary. "Of" means multiply. So you don't know the "what" part, so put a variable. For the variable, we can put x. Then "equals" means the = sign. So, it would look like this: 3/4x=75. Now you solve x. Divide 4 on both sides and you get 3x=300. Now divide 3 on both sides and you get: x=100
So that means x (or "what") would equal 100.
Sources: my brain
I hope this helps. :-)