Instructions: In this task, you need to answer the given multiple-choice question on the physics. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.
Input: Problem: a can do a work in 40 days , b in 60 days . a alone start the work after 10 days he left work . in how many days b can finish the work ?
Options: a ) 20 days , b ) 15 days , c ) 30 days , d ) 45 days , e ) 50 days
Output:
d