Answer: 3/4 = 75/100
Step-by-step explanation: 
3/4 = x/100
(X = unknown number)
You can do cross products by taking the denominator and multiplying by the opposite numerator and doing the same for the numbers left out. 
For example: You would do 4 times X and 3 times 100 which equals 4x = 300 
Then you isolate the variable (x) by dividing 4 by 4 (which is zero) and then dividing 300 by 4 as well (which is 75) 
Then it would be x = 75 
To check you can simplify 75/100