решаем сначала большую скобку:

1) 6 8/15 * 5/14 = 98/15 * 5/14 = 7/3 = 2 1/3,

2) 7 2/3 - 2 1/3 = 5 1/3,

3) 8 3/4 * 2/7 = 35/4 * 2/7 = 5/2 = 2 1/2,

4) 2 1/2 - 1 1/6 = 2 3/6 - 1 1/6 = 1 2/6 = 1 1/3,

5) 5 1/3 : 1 1/3 = 16/3 : 4/3 = 16/3 * 3/4 = 16/4 = 4,

6) 7/18 : 14/27 = 7/18 * 27/14 = 3/4,

7) 3/4 * 4 = 3,

8) 3 - 0,25 = 2,75,

решаем маленькую скобку:

9) 5/6 - 0,75 = 5/6 - 3/4 = 10/12 - 9/12 = 1/12,

находим произведение  обеих скобок:

1/12 * 2,75  = 1/12 * 275/100 = 1/12 * 11/4 = 11/48,

находим сумму:

11/48 + 13/8 = 11/48 + 1 5/8 = 11/48 + 1 30/48 = 1 41/48