66c +98c +9 (8 - 2c) = 78c

66c +98c +9 (8 - 2c) = 78c

66c + 98c + 72 - 18c = 78c

146c = 78c - 72 + 18c

146c - 78c + 18c = -72

86c = -72

c = -72/86

c = -36/43

Ответ: c = -36/43