X-15=5 10+x=55 123:50 100+556

1) Х - 15 = 5 Х = 5 + 15 Х = 20 2) 10 + Х = 55 Х = 55 - 10 Х = 45 3) 123: 50 = 123 : (10 * 5) = 12,3 : 5 = 2,46 4) 100 + 556 = 656