Teacher: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'.
Teacher: Now, understand the problem? Solve this instance: Problem: john was thrice as old as tom 6 years ago . john will be 15 / 13 times as old as tom in 6 years . how old is tom today ?
Options: a ) 5 , b ) 7 , c ) 9 , d ) 11 , e ) 13
Student:
b