There are two approaches:
1. The direct way is to subtract 28 from 58 to determine the number of blue cars, then divide that number by the total number and multiply by 100% to find the percent of blue cars.
i.e. 58 - 28 = 30. 30/58 times 100%.
2. The indirect way is to divide 28 by 58 and multiply by 100% to find the % of white cars, and subtract from 100%.
I hope this helps.