so first of all you have to add
[tex]3 {x}^{2} - 5x + 4 + 8x - 7 \\ 3 {x}^{2} + 3x - 3[/tex]
after getting the sum..you can add the answer( sum )to the given equation(5+3x-×^2)
[tex]3 {x}^{2} + 3x - 3 + 5 + 3 {x} - {x}^{2} \\ {2x}^{2} + 6x + 2[/tex]
therefore your answer is
[tex]2 {x}^{2} + 6x + 2[/tex]
