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 is 1.5 times as fast as b . a alone can do the work in 20 days . if a and b working together , in how many days will the work be completed ? 
Options: a ) 23 , b ) 22 , c ) 12 , d ) 24 , e ) 25
Output:
c