48. 6 9/14 + 4 5/21 − 3 1/42

9/14 = 27/42, 5/21 = 10/42.

6 9/14 + 4 5/21 − 3 1/42 = 7 + (27 + 10 − 1)/42 = 7 6/7.

Ответ: 7 6/7.