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

Ex Input:
Problem: a reduction of 20 % in the price of oil enables a house wife to obtain 4 kgs more for rs . 600 , what is the reduced price for kg ?

Ex Output:
30


Ex Input:
Problem: a 9 % stock yields 8 % . the market value of the stock is :

Ex Output:
rs . 112.50


Ex Input:
Problem: the average of first 10 natural numbers is ?

Ex Output:

5.5