Let's call the sales tax rate "r".
The sales tax on a $30,000 purchase was $2.40, so we can set up an equation:
$30,000 * r = $2.40
To find the sales tax rate, we can divide both sides of the equation by $30,000:
r = $2.40 / $30,000 = 0.008
So, the sales tax rate for this purchase was 0.008, or 0.8%.