day 2

Ryan was working at the summer recreation program. His first job each morning was to lock up the bicycle cage after all the little kids arrived. He enterained himself by counting the number of wheels in the cage each day. Today, Ryan counted a total of 31 vehicles and a total of 84 wheels. If some of the vehicles were Big Wheels(3 wheels), some were bicycles, and some were wagons, how many of each type of vehicle were in the cage?  (答案不唯一)