Answer
$(x+8)(x+2)$
Work Step by Step
Use the hint.
Substituting $(x+1)=u$, the trinomial becomes
$u^{2}+8u+7=$
... Searching for two factors of $+7$ whose sum is $+8,$
we find$\qquad+7$ and $+1.$
= $(u+7)(u+1)$
... bring back x,
$=(x+1+7)(x+1+1)$
= $(x+8)(x+2)$