Answer
12$x^{3}$-10$x^{2}$+15x
Work Step by Step
(11$x^{3}$+15x-9)-(-$x^{3}$+10$x^{2}$-9)
=11$x^{3}$+15x-9+$x^{3}$-10$x^{2}$+9
=11$x^{3}$+$x^{3}$-10$x^{2}$+15x-9+9
=12$x^{3}$-10$x^{2}$+15x
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