Here the dimension of the waxed gymnasium floor is given which is 20 feet by 20 feet. It means the floor is of square shape . And we need to find how many square feet she have to wax. Here square feet is given, which means we have to find the area. SO we need to find the area of the gymansium floor . And area of square is side square. So area of gymnasium floor = 20 ft times 20 ft = 400 square feet .