100 - (h * 8 - 50) = 30
h * 8 - 50 = 100 - 30
h * 8 - 50 = 70
h * 8 = 70 + 50
h * 8 = 120
h = 120 / 8
h = 15
Проверка:
100 - (15 * 8 - 50) = 30
100 - (120 - 50) = 30
100 - 70 = 30
30 = 30
Ответ: h = 15.