$\left ( \color{#FF6800}{ x } \color{#FF6800}{ + } \color{#FF6800}{ 3 } \right ) ^ { \color{#FF6800}{ 2 } } \color{#FF6800}{ - } \color{#FF6800}{ 2 } \left ( \color{#FF6800}{ x } \color{#FF6800}{ + } \color{#FF6800}{ 3 } \right ) \color{#FF6800}{ - } \color{#FF6800}{ 15 }$
$ $ Substitute $ x + 3 $ with $ t$
$\color{#FF6800}{ t } ^ { \color{#FF6800}{ 2 } } \color{#FF6800}{ - } \color{#FF6800}{ 2 } \color{#FF6800}{ t } \color{#FF6800}{ - } \color{#FF6800}{ 15 }$
$\color{#FF6800}{ t } ^ { \color{#FF6800}{ 2 } } \color{#FF6800}{ - } \color{#FF6800}{ 2 } \color{#FF6800}{ t } \color{#FF6800}{ - } \color{#FF6800}{ 15 }$
$ $ Do factorization $ $
$\left ( \color{#FF6800}{ t } \color{#FF6800}{ - } \color{#FF6800}{ 5 } \right ) \left ( \color{#FF6800}{ t } \color{#FF6800}{ + } \color{#FF6800}{ 3 } \right )$
$\left ( \color{#FF6800}{ t } \color{#FF6800}{ - } \color{#FF6800}{ 5 } \right ) \left ( \color{#FF6800}{ t } \color{#FF6800}{ + } \color{#FF6800}{ 3 } \right )$
$ $ Substitute $ t $ with $ x + 3$
$\left ( \left ( \color{#FF6800}{ x } \color{#FF6800}{ + } \color{#FF6800}{ 3 } \right ) \color{#FF6800}{ - } \color{#FF6800}{ 5 } \right ) \left ( \left ( \color{#FF6800}{ x } \color{#FF6800}{ + } \color{#FF6800}{ 3 } \right ) \color{#FF6800}{ + } \color{#FF6800}{ 3 } \right )$
$\left ( \left ( \color{#FF6800}{ x } \color{#FF6800}{ + } \color{#FF6800}{ 3 } \right ) \color{#FF6800}{ - } \color{#FF6800}{ 5 } \right ) \left ( \left ( x + 3 \right ) + 3 \right )$
$ $ Get rid of unnecessary parentheses $ $
$\left ( \color{#FF6800}{ x } \color{#FF6800}{ + } \color{#FF6800}{ 3 } \color{#FF6800}{ - } \color{#FF6800}{ 5 } \right ) \left ( \left ( x + 3 \right ) + 3 \right )$
$\left ( x + 3 - 5 \right ) \left ( \left ( \color{#FF6800}{ x } \color{#FF6800}{ + } \color{#FF6800}{ 3 } \right ) \color{#FF6800}{ + } \color{#FF6800}{ 3 } \right )$
$ $ Get rid of unnecessary parentheses $ $
$\left ( x + 3 - 5 \right ) \left ( \color{#FF6800}{ x } \color{#FF6800}{ + } \color{#FF6800}{ 3 } \color{#FF6800}{ + } \color{#FF6800}{ 3 } \right )$
$\left ( x + \color{#FF6800}{ 3 } \color{#FF6800}{ - } \color{#FF6800}{ 5 } \right ) \left ( x + 3 + 3 \right )$
$ $ Subtract $ 5 $ from $ 3$
$\left ( x \color{#FF6800}{ - } \color{#FF6800}{ 2 } \right ) \left ( x + 3 + 3 \right )$
$\left ( x - 2 \right ) \left ( x + \color{#FF6800}{ 3 } \color{#FF6800}{ + } \color{#FF6800}{ 3 } \right )$
$ $ Add $ 3 $ and $ 3$
$\left ( x - 2 \right ) \left ( x + \color{#FF6800}{ 6 } \right )$