A percent literally means, "per hundred". So 75% is 75% out of 100%. When you're turning a percent into a fraction, the denominator has to be 100.
That means as a fraction, it is 75/100.
Next, you just simplify.
We divide both the numerator and denominator by 25.
75÷25=3
100÷25=4
75% as a fraction in simplest form is 3/4.
Have a nice day! :)