Let
c--------> the total cost
x------> the number of tickets
z------> the cost of one ticket without service fee
we know that
\(108=5.50+5z\)
solve for z
combine like terms
\(5z=108-5.50\)
\(5z=102.50\)
\(z=\$20.50\)
The linear function is equal to
\(c=5.50+20.50x\)
therefore
the answer is
\(c=5.50+20.50x\)
