Verified answer

2 9/13 = 35/13

8.75 = 8 3/4 = 35/4

(2 9/13 - 8.75) : (2 9/13 + 8.75) = (35/13 - 35/4) : (35/13 + 35/4) = (1/13 - 1/4) : (1/13 + 1/4) = - 9/52 : 17/52 = - 9/17

3.2 = 3 1/5 = 16/5

1 1/3 = 4/3

(3.2 - 1 1/3) : (3.2 + 1 1/3) = (16/5 - 4/3) : (16/5 + 4/3) =4* (4/5 - 1/3) : 4*(4/5 +1/3) = (12/5 -5/15) : (12/15 + 5/15) = 7/15  : 17/15 = 7/17

-9/17 : 7/17 = - 9*17/(17*7) = -   9/7