[SOLVED] Simplification of Algebraic fractions

Q. Simplify:

$\displaystyle \frac {(a + b)^2 - c^2} {3a + 3b - 3c}$

i've got up to

$\displaystyle \frac {a^2 + 2ab +b^2 - c^2} {3(a + b - c)}$

but i can't simplify it further unless $\displaystyle \frac {a^2 + 2ab +b^2 - c^2} {3(a + b - c)}$ is replaced by $\displaystyle \frac {a^2 + b^2 - c^2}{3(a + b - c)}$ then i could work my way to the answer, but im not sure if that should be the right method

because of the rule, $\displaystyle (a + b)^2 = a^2 + 2ab + b^2$

btw the answer is $\displaystyle \frac {a + b - c}3$