что такое равные фигуры?

из демонстрационного врианта егэ по английскому. 

B8 I remember my last year at shool very well. There were three boys (name) William in my class .
B9 Miss Fisher, one of the teachers, called them all William, and we (not know) which one she was talking to.

B10. One day, during a lesson on efficiency, she thundered, " William, put that gum you (chew) in the wastepaper bin at once!"