Paula writes and mails 10 checks each month to pay her bills. Each check requires a first-class stamp, which costs 55 cents. Therefore, the monthly cost of mailing checks is 10 checks * $0.55 = $5.50. Over a year, this amounts to $5.50 * 12 months = $66. Since her bank offers free use of its bill payment system, by using this system, Paula avoids the $66 cost of stamps, resulting in a total savings of $66 per year.