Task: Question Answering
Input (English): Problem: a person purchases 90 clocks and sells 40 clocks at a gain of 10 % and 50 clocks at a gain of 20 % . if he sold all of them at a uniform profit of 15 % , then he would have got rs . 40 less . the cost price of each clock is : ? 
Options: a ) 40 , b ) 60 , c ) 80 , d ) 67 , e ) 30
Output (English): c