Answer:
[tex] 3 {x}^{2} + 12x + 5[/tex]
Step-by-step explanation:
[tex](x^2 + 3x) + (2x^2 + 9x + 5) \\ \\ = x^2 + 3x + 2x^2 + 9x + 5 \\ \\ = {x}^{2} + 2 {x}^{2} + 3x + 9x + 5 \\ \\ = 3 {x}^{2} + 12x + 5[/tex]
