`a) 11/12 - 29/35 + 1/4 - 41/35`

`= (11/12 + 1/4) - (29/35 + 41/35)`

`= (11/12 + 3/12) - 70/35`

`= 14/12 - 2`

`= 7/6 - 2`

`= 7/6 - 12/6`

`= -5/6`

`b) (1/15 - 3/5) : 5/6 - (11/15 - 8/5) : 5/6`

`= [(1/15 - 3/5) - (11/15 - 8/5)] : 5/6`

`= (1/15 - 3/5 - 11/15 + 8/5) : 5/6`

`= [(1/15 - 11/15) + (8/5 - 3/5)] : 5/6`

`= (-10/15 + 5/5) : 5/6`

`= (-2/3 + 1) : 5/6`

`= 1/3 : 5/6`

`= 1/3 * 6/5`

`= 2/5`

`c) 5/6 : (4/15 - 3/5) - 5/6 : (11/15 + 8/5)`

`= 5/6 : (4/15 - 9/15) - 5/6 : (11/15 + 24/15)`

`= 5/6 : (-5/15) - 5/6 : (35/15)`

`= 5/6 : (-1/3) - 5/6 : (7/3)`

`= 5/6 * (-3) - 5/6 * 3/7`

`= -5/2 - 5/14`

`= -35/14 - 5/14`

`= -40/14`

`= -20/7`