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

Ex Input:
Problem: a customer went to a shop and paid a total of $ 40 , out of which $ 1.28 was for sales tax on taxable purchases . if the tax rate was 8 % , then what was the cost of the tax free items ?

Ex Output:
$ 22.72

Ex Input:
Problem: the total marks obtained by a student in mathematics and physics is 32 and his score in chemistry is 20 marks more than that in physics . find the average marks scored in mathamatics and chemistry together .

Ex Output:
26

Ex Input:
Problem: what is the units digit of 23 ^ 2 * 17 ^ 2 * 39 ^ 2 ?

Ex Output:
1