In chapter 5, what trick did they decide to play on Janice Avery?

The big bully Janice has been throwing her weight around as usual. This time, she's been picking on Mae Belle, stealing the Twinkies her dad gave her. Mae Belle would like nothing more than for Jess to give Janice a good hiding. But beating up on a girl is not really a good idea—and besides, Jess and Leslie come up with a much better way of getting back at the bully. They know that Janice has a major crush on Willard Hughes, so they plan to write her a love letter claiming to be from Willard. The idea is that when Janice opens her big mouth about the letter—which she will—then she'll be publicly humiliated, exposed as a liar and a fantasist.
The plan works a treat. Janice's friend Wilma loudly tells everyone who'll listen that Janice has a date with Willard. A boy on the bus accuses her of being a liar, and they get into a big fight. Jess and Leslie wanted to get revenge on Janice by making her look like a complete fool in front of the other kids, and they've certainly done that.