Xiao Ming plays the small square first, and then the small square has to wait 16+12+16 minutes, and the other three wait 16+ 14+ 12 and/kloc respectively.

So let Xiao Fang hit Xiao Hong first, then Xiao Gang and Xiao Ming, and the waiting time is.

10, 10+ 12, 10+ 12+ 14, 10+ 12+ 14.