The above expression is not in its simplest form, and we need to simplify it, that is what asked in the question.
Given equation,
[tex](9 {x}^{2} - 3x + 7) + ( - 3 {x}^{2} + 2)[/tex]
First of all, let's open the parentheses to combine the like terms for simplifying.
[tex]9 {x}^{2} - 3x + 7 - 3 {x}^{2} + 2[/tex]
Arranging the like terms, x² with x², x with x and constant terms near to each other.
[tex]9 {x}^{2} - 3 {x}^{2} - 3x + 7 + 2[/tex]
Simplying further,
[tex](9 - 3) {x}^{2} - 3x + 9[/tex]
[tex]6 {x}^{2} - 3x + 9[/tex]
So, the correct option is C
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