80*7-42: (50786-50780) * 9 = 7*4+64:8 * (21-17) + 30000 = 54:6+540:6+5400:6=

Первый пример.

80 * 7 - 42 : (50 786 - 50 780) * 9 = 497;

50 786 - 50 780 = 6;

42 / 6 = 7;

7 * 9 = 63;

80 * 7 = 560;

560 - 63 = 497;

Второй пример.

7 * 4 + 64 : 8 * (21 - 17) + 30 000 = 30 060;

21 - 17 = 4;

64 / 8 = 8;

8 * 4 = 32;

7 * 4 = 28;

28 + 32 = 60;

60 + 30 000 = 30 060;

Третий пример.

54 : 6 + 540 : 6 + 5400 : 6 = 999;

54 / 6 = 9;

540 / 6 = 90;

5400 / 6 = 900;

9 + 90 = 99;

99 + 900 = 999;