Question

photographic reprints cost 0.52 each at a local photo shop, or 0.4r each plus 1.15 postage and handling, through the mail. how many reprints must a customer purchase to make it less expensive to use mail order

Answer 1

Mail order cost for n prints will be
  m = 0.40n +1.15
Photo shop cost for n prints will be
  p = 0.52n

Mail order cost will be less than photo shop cost when
  m < p
  0.40n +1.15 < 0.52n
  1.15 < 0.12n
  9.583 < n

A customer must purchase 10 or more prints to make it less expensive to use mail order.