Given the task definition and input, reply with output. 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'.

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

a