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

Ex Input:
Problem: find the principle on a certain sum of money at 9 % per annum for 2 2 / 5 years if the amount being rs . 1120 ?

Ex Output:
921.0

Ex Input:
Problem: the average weight of a , b and c is 60 kg . if the average weight of a and b be 70 kg and that of b and c be 50 kg , then the weight of b is :

Ex Output:
60 kg

Ex Input:
Problem: 10 + 19

Ex Output:
29