`a, (-5)/9 + 8/15 + (-2)/11 + 4/(-9) + 7/15`
`= ((-5)/9 + 4/(-9)) + (8/15 + 7/15) + (-2)/11`
`= ((-5)/9 + (-4)/9) + 15/15 + (-2)/11`
`= (-9)/9 + 1 + (-2)/11`
`= -1 + 1 + (-2)/11`
`= 0 + (-2)/11`
`= (-2)/11`
`b, (10 2/9 + 2 3/5) - 5 2/9`
`= 10 2/9 + 2 3/5 - 5 2/9`
`= (10 2/9 - 5 2/9) + 2 3/5`
`= (10 + 2/9 - 5 - 2/9) + 13/5`
`= (10 - 5) + 13/5`
`= 5 + 13/5`
`= 25/5 + 13/5`
`= 38/5`
`c, 9 5/13 - (2/5 + 4 5/13)`
`= 9 5/13 - 2/5 - 4 5/13`
`= (9 5/13 - 4 5/13) - 2/5`
`= (9 + 5/13 - 4 - 5/13) - 2/5`
`= (9 - 4) - 2/5`
`= 5 - 2/5`
`= 25/5 - 2/5`
`= 23/5`