We can write all information we have as:
81 answers = x% of 450 students
So we just need to do a simple equation:
81 = x% * 450
81 =

* 450
81 =

* 45
81 =

/ * 10 (both sides)
810 = 45x / ÷ 45 (both sides)
x = 18 [percent]Answer: 18% of the students preferred country music.