Х + 6/7 * Х + 6/7 * Х + 3 = 79;

Найдем х.

x * (1 + 6/7 + 6/7) + 3 = 79;

x * (7/7 + 12/7) + 3 = 79;

x * (19/7) + 3 = 79;

19/7 * x = 79 - 3;

19/7 * x = 76;

19 * x = 7 * 76;

19 * x = 532;

x = 532/19;

x = 28.