Answer
$\frac{3}{x-3}$
Work Step by Step
Since both expressions have common denominators, you can simply combine their numerators.
$\frac{x^2+3x}{x^2+x-12}-\frac{x^2-12}{x^2+x-12}$
$\frac{3x+12}{x^2+x-12}$
$\frac{3(x+4)}{(x+4)(x-3)}$
$\frac{3}{x-3}$
