1) х*81+67=553 2) 489+с*5=9614 3) а * (288-190) = 392 4) 240:а=480:80

Вычислим переменные в уравнениях.

1) х * 81 + 67 = 553;

81 * x = 553 - 67;

81 * x = 440 + 46;

81 * x = 486;

x = 486/81;

x = 6.

2) 489 + с * 5 = 9 614;

5 * c + 489 = 9 614;

5 * c = 9 614 - 489;

5 * c = 9 125;

c = 9 125/5;

c = 1 000 + 800 + 20 + 5;

c = 1 825;

3) а * (288 - 190) = 392;

a * (100 - 10 + 8) = 392;

98 * a = 392;

a = 392/98;

a = 4.

4) 240/а = 480/80;

1/a = 2/80;

1/a = 1/40;

a = 40.