#### Answer

$x=-5$ and $x = 1$ are the critical numbers.

#### Work Step by Step

Find the critical numbers of $x^3 + 6x^2 - 15x$
Differentiate and set the derivative $=0$.
$f'(x) = 3x^2+12x-15$
$0=3(x^2+4x-5)$
$0=3(x-1)(x+5)$
$x=-5$ and $x = 1$ are the critical numbers.