#### Answer

$x^{2}$ + 9x

#### Work Step by Step

(-3$x^{2}$ + x) + (4$x^{2}$+ 8x)
The like terms are -3$x^{2}$ and 4$x^{2}$ containing the same variable to the same power($x^{2}$), as well as x and 8x (both containing x) .
We begin by grouping these pairs of like terms.
( -3$x^{2}$ + 4$x^{2}$)+(x + 8x)
= $x^{2}$ + 9x