1) x = (20 - 10) : 2 = 5
2) x = (60 - 40) : 4 = 5
3) x = (4/5 - 1/5) : 2/5 = 0.3 = 3/10
4) x = 5, y = 6; или x = 10, y = 4; или x = 15, y = 2
