419 – 20 · 7 = 419 – 140 = 279
6 · 70 – 285 = 420 – 285 = 135
378 + 50 · 40 – 1800 = 378 + 2000 – 1800 = 578
80 · (140 – 80) + 570 = 80 · 60 + 570 = 4800 + 570 = 5370
80 · 20 + 769 – 684 = 1600 + 769 – 684 = 1685
576 + 720 : 9 – 578 = 576 + 80 – 578 = 78