Add the sum of the numbers (−5.4) and (+8.2) to the opposite number of (−2 3/4 ).

The number are (−5.4) and (+8.2).
Sum of these two numbers are = (−5.4) + (+8.2)
= -5.4 + 8.2
= 2.8
Now we are going to add this to the opposite number of (−2 3/4 ).
(−2 3/4 ) = -11/4 = -2.75
now opposite number of -2.75 is 2.75
Thus, 
2.8 + (2.75)
= 2.8 + 2.75
= 5.55