`a) 1/3 - 5/6 + 7/12`
`= 4/12 - 10/12 + 7/12`
`= 1/12`
``
`b) 1/3 - 5/4 . 4/15`
`= 1/3 - 1/3`
`= 0`
``
`c) 7/19 . 8/11 + 7/19 . 5/11 - 2/11 . 7/19`
`= 7/19 . ( 8/11 + 5/11 - 2/11)`
`= 7/19 . 1`
`= 7/19`
``
`d) 4/7 + 15/7 : 5 -4 3/5`
`= 4/7 + 3/7 - 23/5`
`= 1 - 23/5`
`=-18/5`