(5.7 + 8.8) / 2.9 + x / 10.1 = 9

14.5 / 2.9 + x / 10.1 = 9

5 + x / 10.1 = 9

x / 10.1 = 4

x = 4 * 10.1

x = 40.4

Ответ: x = 40.4