Hi,
Melanie can paint a certain barn by herself in X days. Milissa in 2x days.
the fractional part of the barn,that they complete in one day by working together.
1/x + 1/2x
x = 5
1/5 + 1/10 = 2/10 + 1/10 = 3/10 of the barn can be painted in one day working together.
(3 1/10 days to finish it)