6целых2/3-8,75-2целых5/12 решите 50 !

-6 2/3 - 8,75 - 2 5/12 = 
= -20/3 - 875/100 - 29/12 = 
= - (20/3 + 875/100 + 29/12) = 
= - (2000/300 + 2625/300 + 725/300) = 
= - 5350/300 = 
= - 107/6 = - 17 5/6,

или:

-6 2/3 - 8,75 - 2 5/12 = 

1) -6 2/3 - 2 5/12 = -(20/3 + 29/12) = - (80/12 + 29/12) = - 109/12 = - 9 1/12,
2) - 8,75 - 9 1/12 = - 8 3/4 - 9 1/12 = - (35/4 + 109/12) = -(105/12 + 109/12) = 
    = - 214/12 = - 17 10/12 = - 17 5/6