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'.

Example Input: Problem: the toll for crossing a certain bridge is $ 0.75 each crossing . drivers who frequently use the bridge may instead purchase a sticker each month for $ 11.00 and then pay only $ 0.30 each crossing during that month . if a particular driver will cross the bridge twice on each of x days next month and will not cross the bridge on any other day , what is the least value of x for which this driver can save money by using the sticker ? 
Options: a ) 14 , b ) 15 , c ) 16 , d ) 28 , e ) 29
Example Output: e

Example Input: Problem: find the ones digit of 73 ^ 356 
Options: a ) 1 , b ) 5 , c ) 6 , d ) 7 , e ) 9
Example Output: a

Example Input: Problem: if 16 ^ 5 * 15 ^ 4 * 14 ^ 3 * 13 ^ 2 = x , what is the units digit of x ? 
Options: a ) 2 , b ) 3 , c ) 6 , d ) 5 , e ) 0
Example Output:
e