#### Explanation:

The number of cars ($c$) in a parking lot increases when the parking fee ($f$) decreases.

This indicates inverse variation. We can write the proportionality equation as :

$c \propto \frac{1}{f}$

And the equation after removing the proportionality sign can be written as :

$c = k \times \frac{1}{f}$ , where $k$ is the proportionality constant.

The number of cars when the fee is $6 will be : $c = \frac{k}{6}\$