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'.

Problem: a and b together can complete a work in 12 days . a alone can complete it in 20 days . if b does the work only for half a day daily , then in how many days a and b together will complete the work ?
Options: a ) 10 days , b ) 11 days , c ) 15 days , d ) 20 days , e ) none of these
c