#### Answer

$3x^{2}+3xh+h^{2}$

#### Work Step by Step

We apply the binomial theorem to expand $(x+h)^3$:
$(x+h)^3=x^{3}+3x^{2}h^1+3x^1h^{2}+h^{3}$
Now we simplify:
$\displaystyle \frac{(x+h)^{3}-x^{3}}{h}=\frac{x^{3}+3x^{2}h+3xh^{2}+h^{3}-x^{3}}{h}=\frac{3x^{2}h+3xh^{2}+h^{3}}{h}=\frac{h(3x^{2}+3xh+h^{2})}{h}=3x^{2}+3xh+h^{2}$