Answer
$(3x+1)(x+5)$
Work Step by Step
Find factors of $ac$ that have a sum of $b$.
Since $ac=15$ and $b=16$,
find factors of $15$ with a sum of $16$.
$\left[\begin{array}{lll}
\text{Factors of 15 } & \text{Sum of factors} & \\
1\text{ and }15 & 16 & \text{...what we need}
\end{array}\right]$
$3x^{2}+16x+5$
...use the factors to rewrite $bx$.
$=3x^{2}+x+15x+5$
...factor out the GCF out of each pair of terms.
$=x(3x+1)+5(3x+1)$
...use the Distributive Property.
$=(3x+1)(x+5)$
