Let's start with an example.
At the market, 8 batteries cost $10.
How much do 6 batteries cost?
We’re trying to find the cost of 6 batteries.
Batteries Cost
8 / 8 = 1 $10/ 8 = $1.25
If 8 batteries cost $10, then 11 battery costs $1.25.
Batteries Cost
8 $10
1 x 6 $1.25 x 6
6 $7.50
So, 6 batteries cost $7.50.
Back to your question...
We are trying to find the rate of fair which means the fair price for 1 person
Fair Person
18/3 3/3
6 1
So, the fair owner will make $6 for 1 person.
Hope this helped! Good luck!