The numbers of cars (c) in the parking lot increases when the parking fee (f) decrease. write the correct equation for this scenario and solve for the number of cars when the fee is $6

So when one goes up, the other goes down. This is an inverse equation.

An inverse equation looks like this: y = 1/x

In this case, when parking fee (f) decreases, cars (c) increase.
You know which side to put each variable on using the chart they gave you.
f         | c
20.00  15        (20.00 = x/15) x=300
30.00  10        (30.00 = x/10) x=300

So your equation in this case is f = 300/c
Knowing that, plug in the fee of 6.00

6 = 300/c   Multiply both sides by c.
6c = 300    Divide both sides by 6.
c = 50 cars