Definition: In this task, you need to answer the given multiple-choice question on the general math. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.
Input: Problem: a manufacturer produces a certain men ' s athletic shoe in integer sizes from 8 to 17 . for this particular shoe , each unit increase in size corresponds to a 1 / 5 - inch increase in the length of the shoe . if the largest size of this shoe is 20 % longer than the smallest size , how long , in inches , is the shoe in size 15 ?
Options: a ) 8.6 , b ) 9.8 , c ) 10.4 , d ) 11.2 , e ) 12.6
Output:
c