`a) -5/7. 2/11 + -5/7: 11/9 + 1 5/7`
`= -5/7. 2/11 + -5/7. 9/11 + 1 5/7`
`= -5/7. (2/11 + 9/11) + 1 5/7`
`= -5/7. 1 + 1 5/7`
`= -5/7 + 1 5/7`
`= 1`
`b) (-8/13 : 3/7 + -5/13 : 3/7). ( (-4)^3. |-3|) /7`
`= [ (-8/13 - 5/13) : 3/7)]. (-64. 3)/7`
`= (-1 : 3/7). (-192)/7`
`= -7/3. (-192)/7`
`= 64`
`c) 4/17. (7 3/4 - 6 1/3) + (5 3/4 - 6,95) : (-1 3/5)`
`= 4/17. (31/4 - 19/3) + (23/4 - 139/20) : -8/5`
`= 4/17. 17/12 + -6/5. -5/8`
`= 1/3 + 3/4`
`= 13/12`