Presuming that "survey 3,000" is the total and "900" is the factor who had problems then dividing the total amount by the amount of problems like equal the relative frequency of people that had problems
Math:
Amount of people you had problems / Amount of people who bought the new car.
900 / 3000 = 0.3
Now you need to multiply by 100% (because % in this case is a unit/measurement)
