A local coupon mailer charges $9 for each of the first four lines of an ad and $6 for
each additional line.
Let x represent the number of lines in the ad, and c(x) represent the cost of an ad as a
piecewise function.
c(x) = 9x
36 + 6(x-4)
$
when x ≤ 4
when x >4
a. What is the price of a six-line ad?
b. What is the price of a four-line ad?
c. What are the coordinates of the cusp of the piecewise function?