find the sum of2 3/4 and 2 4/5.find the differnce between this sum and 6

First, find the common denominator.

2 3/4 = 2 15/20
2 4/5 = 2 16/20

2 15/20 + 2 16/20 = 4 31/20 = 5 11/20

6 = 5 20/20

5 20/20 - 5 11/20 = 9/20