arithmetic - varun can do a piece of work in 80 days he works at it for 10 days and then tarun alone finishes the remaining work in 42 days the two together could complete the work in - skillgun

Let A = Varun, B = Tarun.
Work done by A in 10 days = (1/80) * 10 = 1/8
Remaining work=(1 - (1/8)) = 7/8
Now, 7/8 work is done by B in 42 days
Whole work will be done by B in 42 * (8/7) = 48 days.
As 1 days work = 1/80 and B's 1 days work = 1/48
(A + B)’s 1 days work = [(1/80) + (1/48)] = 8/240 = 1/30
so, both will finish the work in 30 days.