Simplify (x^2+3x)+(-2x^2+9x+5)

$(x^{2} + 3 x) + (- 2 x^{2} + 9 x + 5)$

Remove parentheses.

$x^{2} + 3 x - 2 x^{2} + 9 x + 5$

Subtract $2 x^{2}$ from $x^{2}$ .

$- x^{2} + 3 x + 9 x + 5$

Add $3 x$ and $9 x$ .

$- x^{2} + 12 x + 5$