Concept:If Amar is thrice as good a workman as Vikram, Amar’s time is 31​ of Vikram’s time.Explanation:Let Vikram alone take x days to complete the work.Then Amar alone takes x−80 days.Since Amar’s time : Vikram’s time =1:3,x−80=3x​3x−240=x2x=240, so x=120 days.Hence Vikram takes 120 days and Amar takes 40 days.Work done by both in one day:1201​+401​=1201+3​=1204​=301​So together they can finish the work in 30 days.Answer:30 days, i.e. option D.