720 : 9 = 80
16 : 8 = 2
80 * 3 = 540 - 30 (240 = 540 - 300)
80 * 5 = 100 * 4 (400 = 400)
400 - 40 = 60 * 6 (360 = 360)
210 : 7 = 15 * 2 (30 = 30)
320 : 8 = 360 : 9 (40=40)