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: Problem: what is difference between biggest and smallest fraction among 2 / 3 , 3 / 4 , 4 / 5 and 5 / 3 
Options: a ) 2 / 5 , b ) 3 / 5 , c ) 1 / 6 , d ) 1 , e ) none of these
Example solution: d
Example explanation: "explanation : 2 / 3 = . 66 , 3 / 4 = . 75 , 4 / 5 = . 8 and 5 / 3 = 1.66 so the biggest is 5 / 3 and the smallest is 2 / 3 their difference is 5 / 3 - 2 / 3 = 3 / 3 = 1 option d"

Problem: Problem: if a = 105 and a ^ 3 = 21 * 49 * 45 * b , what is the value of b ? 
Options: a ) 25 , b ) 42 , c ) 45 , d ) 49 , e ) 54

Solution: a