`\text{a)}`
`(13 4/9 + 2 1/9 ) - 3 4/9`
`= (13 + 4/9 + 2 +1/9) - 3 4/9`
`= 15 + 5/9 - 3 4/9`
`= (15-3) + (5/9 - 4/9)`
`= 12 1/9`
`= 109/9`
$\\$
`\text{b)}`
`2/3 +1/5 . 10/7`
`= 2/3 + 10/35`
`= 2/3 + 2/7`
`= 14/21 + 6/21`
`= 20/21`
$\\$
`-7/11 . 4/13 - 7/11 . 9/13 + 2 7/11`
`= 7/11 . (-4/13) - 7/11 . 9/13 + 2 7/11`
`= 7/11(-4/13 - 9/13) +2 7/11`
`= -7/11 + 2 7/11`
`= (-7/11 +7/11) +2`
`= 2`