The easiest way to look at this is to either change 3/4 to a decimal (which is 0.75) or change 25% to a fraction (which is 25/100). Using the language of mathematics, write in symbols what you have:
3/4 is (= ) 25/100 of (times) what (? or x or some other variable)
Then you have 3/4 = 25/100 * x
To find x, divide by the coefficient (number) times x on both sides
3/4 div 25/100 = 25/100 div 25/100 times x
To divide, invert and multiply
3/4 * 100/25 = x
3/4 * 4/1 = x
3 = x which is the solution to your problem.