Answer
-5$x^{2}$-11x+13
Work Step by Step
The phrase, "Add (6$x^{2}$-7) and (-11$x^{2}$-11x+20)." can be translated to the expression: (6$x^{2}$-7)+(-11$x^{2}$-11x+20)
Simplify:
(6$x^{2}$-7)+(-11$x^{2}$-11x+20)
=6$x^{2}$-7-11$x^{2}$-11x+20
=6$x^{2}$-11$x^{2}$-11x-7+20
=-5$x^{2}$-11x+13