Answer:
the cost of an order for 5 books=15x-21
Step-by-step explanation:
a mail order catalog lists books for 3x - 5 dollars each.
i.e. cost of 1 book=3x-5
Hence, cost of 5 books=5×(3x-5)=$(15x-25)
also the cost of postage is $2 for 3 books or less.
as there are 5 books so we have to make two postages.
Hence, cost of postage for 5 books=$4
Hence, the total cost of an order of 5 books=15x-25+4
=15x-21.
