If there are several plausible solutions, be sure to explain why the solution you favor is better than the other solutions. Be sure to turn in your exam with your bluebooks. You need a jar of peanut butter. You go to the supermarket to buy it.
S sends back a printed brochure, on the back of which is a price list that includes pencils.
S has circled the price for pencils. S receives B's purchase order three days after it was sent. S then promptly ships the pencils without sending any acknowledgment. A week later, S bills B at the higher price. B contests the bill.