The task is to generate the correct answer for a given math problem.

Example Input: Problem: robert ' s salary was decreased by 20 % and subsequently increased by 20 % . how much percentage does he lose ?
Example Output: 4 %

Example Input: Problem: meena wrote all the numbers from 1 to 29,999 inclusive . how many digits did she write in total ?
Example Output: 138,889

Example Input: Problem: the average height of 20 students in a class was calculated as 175 cm . it has later found that the height of one of the students in the class was incorrectly written as 151 cm whereas the actual height was 136 cm . what was the actual average height of the students in the class ?
Example Output:
174.25 cm