`1)`
`a) 2/3 + 1/5 - 10/7`
`= 70/105 + 21/105 - 150/105`
`=-59/105`
``
`b) (-3)/7 + 15/26 + ((-2)/13 + 3/7)`
`= (-3)/7 + 15/26 - 2/13 + 3/7`
`= ((-3)/7 + 3/7) + ( 15/26 - 2/13)`
`= 0 + 11/26`
`= 11/26`
``
`c) (-5)/9 + 5/9 : ( 3 1/3 - 1 2/3)`
`= (-5)/9 + 5/9 : 5/3`
`= (-5)/9 + 1/3`
`= -2/9`
``
`d) (-4)/5 . 11/13 + 4/5 . (-2)/13 - 1/5`
`= (-4)/5 . 11/13 + (-4)/5 . 2/13 - 1/5`
`= (-4)/5 . ( 11/13 + 2/13) - 1/5`
`= (-4)/5 . 1 - 1/5`
`= -4/5 - 1/5`
`= -1`