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

Example Input: Problem: given that p is a positive even integer with a positive units digit , if the units digit of p ^ 3 minus the units digit of p ^ 2 is equal to 0 , what is the units digit of p + 4 ?
Example Output: 10

Example Input: Problem: a 9 % stock yields 8 % . the market value of the stock is :
Example Output: rs . 112.50

Example Input: Problem: a present value of a machine is $ 1000 . its value depletiation rate is 10 % per annum then find the machine value after 2 years ?
Example Output:
$ 810