A short math joke

On Valentine's Day, someone knocked at the door, and the wife opened the door and saw that it was a courier. The wife was a little surprised: "My husband must have bought himself a present on Valentine's Day." The courier took out a list and said, "Your husband entrusted the courier company to send a bunch of flowers, and he asked you to sign it and pay the expenses listed above." The wife asked curiously, "Where are the flowers?" The courier said, "We have already sent it!"