Hey there! :)
Since both mixed numbers are negative, the answer will be negative. You can just remove the (-) sign and add first. After you add, put the negative sign
8 3/4 + 11 1/3
Change the fractions by using a common denominator: 12
8 3/4 = 8 9/12
11 1/3 = 11 4/12
Now, add
8 9/12 + 11 4/12 = 19 13/12 = 20 1/12
Add the (-) sign → -20 1/12
Answer ⇒ -20 1/12
:)