#### Explanation:

Nine chickens laying an average of six eggs per week will lay totally $x$ number of eggs in two weeks:

$x = 9 \times 6 \times 2$

$x = 108$

$108$ divided by $12$ is $9$, which means that Gregory sold $9$ dozen eggs in two weeks.

At the rate of $3 per dozen, Gregory collected: $9 \times 3 = 27\$