Q. Simplify:

$\displaystyle \frac {4}{21 - 9x} \div \frac {8}{14 - 6x}$

this is the furthest i've gotten

$\displaystyle \frac {4}{9(3 - x)} \times \frac {2(7 - 3x)}{8}$

the answer is: $\displaystyle \frac 1 3$

im not even sure if my working out so far is right .

thanks