`11)`
`8/40 + (-36)/45`
`= 1/5 - 4/5`
`= -3/5`
``
`12)`
`3/5 + 4/(-7)`
`= 3/5 - 4/7`
`= 21/35 - 20/35`
`= 1/35`
``
`13)`
`4/9 - (-5)/6`
`= 4/9 + 5/6`
`= 8/18 + 15/18`
`= 23/18`
``
`14)`
`6/7 + 1/7 . 2/7 + 1/7 . 5/7`
`= 6/7 + 1/7 . ( 2/7 + 5/7)`
`= 6/7 + 1/7 . 1`
`= 6/7 + 1/7`
`= 1`
``
`15)`
`4/9 . 13/3 - 4/3 . 40/9`
`= 4/9 . 13/3 - 4/9 . 40/3`
`= 4/9 . ( 13/3 - 40/3)`
`= 4/9 . (-9)`
`= -4`
``
`16)`
`8 2/7 - (3 4/9 + 4 2/7)`
`= 8 2/7 - 3 4/9 - 4 2/7`
`= ( 8 2/7 - 4 2/7) - 3 4/9`
`=4 - 3 4/9`
`= 5/9`
``
`17)`
`( 10 2/9 + 2 3/5)- 6 2/9`
`= 10 2/9 + 2 3/5 - 6 2/9`
`= ( 10 2/9 - 6 2/9) + 2 3/5`
`= 4 + 2 3/5`
`=6 3/5`
``
`18)`
`7/19 . 8/11 + 7/19 . 3/11 - 26/19`
`= 7/19 . ( 8/11 + 3/11) - 26/19`
`= 7/19 . 1 - 26/19`
`= 7/19 - 26/19`
`= -1`
