Instructions: 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: the ages of two persons differ by 16 years . if 6 years agao , the elder one be 3 times as old as the younger one , find their present ages .
Options: a ) 20 years . , b ) 30 years . , c ) 40 years . , d ) 50 years . , e ) 60 years .
Output:
b