Answer by JKismyhusbandbae: (I don't know if you wanted me to factor because you weren't specific but you can't simplify this.)
[tex]\mathrm{Factor}\:9a+18\\9a+18\\\mathrm{Rewrite\:}18\mathrm{\:as\:}9\cdot \:2\\=9a+9\cdot \:2\\\mathrm{Factor\:out\:common\:term\:}9\\=9\left(a+2\right)[/tex]
