Task: Question Answering
Input (English): Problem: in assembling a bluetooth device , a factory uses one of two kinds of modules . one module costs $ 10 and the other one , that is cheaper , costs $ 2.5 . the factory holds a $ 62.50 worth stock of 22 modules . how many of the modules in the stock are of the cheaper kind ? 
Options: a ) 31 , b ) 35 , c ) 21 , d ) 40 , e ) 45
Output (English): c