Task: Question Answering
Input (English): Problem: a customer went to a shop and paid a total of $ 30 , out of which 90 cents was for sales tax on taxable purchases . if the tax rate was 6 % , then what was the cost of the tax free items ? 
Options: a ) $ 12.70 , b ) $ 13.20 , c ) $ 14.10 , d ) $ 15.60 , e ) $ 16.80
Output (English): c