Answer
$=\displaystyle \frac{3(3x+13)}{(x+4)(x+5)}, \quad x\neq-4,-5$
Work Step by Step
The denominators are different.
Find a common denominator.
LCD=$(x+4)(x+5)$
$\displaystyle \frac{3}{x+4}+\frac{6}{x+5}$=$\displaystyle \frac{3(x+5)}{(x+4)(x+5)}+\frac{6(x+4)}{(x+4)(x+5)}$
$=\displaystyle \frac{3x+15+6x+24}{(x+4)(x+5)}$
$=\displaystyle \frac{9x+39}{(x+4)(x+5)}$
$=\displaystyle \frac{3(3x+13)}{(x+4)(x+5)}$
... exclude values that yield 0 in the denominator:
$x\neq-4,-5$
... and, cancel common factors (here, there are none)
$=\displaystyle \frac{3(3x+13)}{(x+4)(x+5)}, \quad x\neq-4,-5$
