#### Answer

-11$r^{4}$ + r

#### Work Step by Step

(7$r^{4}$+5$r^{2}$ + 2r) + (-18$r^{4}$ -5 $r^{2}$ -r)
The like terms are 7$r^{4}$ and -18$r^{4}$ (both containing $r^{4}$) , 5$r^{2}$ and -5 $r^{2}$ (both containing $r^{2}$) , 2r and -r (both containing r).
We begin by grouping these pairs of like terms
=(7$r^{4}$ -18$r^{4}$) + (5$r^{2}$ - 5 $r^{2}$) + ( 2r - r)
= -11$r^{4}$ + r