5 3/7 14/19 = 38/7 14/19 = 532/133 = 4

3 6/8 ÷ 7.25 = 30/8 ÷ 7.25 = 15/4 ÷ 29/4 = 15/4 * 4/29 = 60/116 = 15/29

8.4 + 4 = 12.4

Ответ: 12.4