5 4/14 +3 5/13=======
(5*14 + 4)/14 + (3*13+5)/13 =74/14 + 44/13 = (74*13 + 44*14)/(13*14) = 1578/182 примерно равно 8.6
5+3=8 целых. 4/14+5/13= (4*13+5*14)/13*14 = 8 целых 61/91