In Hoot, what type of bicycle does Beatrice ride when she goes to Roy's house to get "science experiment materials?"

After Beatrice rescues Roy from being pulverized by Dana Matherson in the janitor's closet, she steals a bike from the rack at Trace Middle School and has Roy sit on the handle bars. She pedals with Roy on the handle bars to his house where his mother greets them. They get the medical supplies and hamburger, telling Roy's mother the meat is for a science experiment, and bike to the junk yard where the wounded Mullet Fingers is hiding out. After tending to Mullet Fingers's infected arm, the three teens head over to the Mother Paula's construction site, and Mullet Fingers shows them the owls. However, Mullet Fingers becomes dizzy climbing the fence to leave the site, and Beatrice slings him over the handle bars of the bike with Roy running behind. When Officer Delinko spots them, Beatrice ditches the bicycle and runs away carrying Mullet Fingers. Roy pursues them, leaving the policeman to pick up the bike. He brings it with him when he goes to visit Roy's parents. Roy's father says that the bike isn't Roy's, but his mother recognizes it as the one that Roy's friend had been riding. It was a "blue beach-cruiser" model. Before Mrs. Eberhardt can decide whether to admit she has seen the bike before, she gets a call from the emergency room saying her son has been injured.