$9
Explanation
Step 1
total cost:
[tex]total\cos t=4x+36[/tex]it measn
you have a linear function where
4 is the slope ( the cost per person)
36( the y itercept)
[tex]36=\text{ admission fee for the four friends}[/tex]so, the admission fee for one person
[tex]\text{admision f}e=\frac{36}{4}=9[/tex]I hope this help you