`c) 4 7/12 - ( 11 1/24 + 5 7/12)`
`= 4 7/12 - 11 1/24 - 5 7/12`
`= ( 4 7/12 - 5 7/12) - 11 1/24`
`= -1 - 11 1/24`
`= -12 1/24`
`=-289/24`
``
`d) 3/7 : 21/4 - 3/7 : 13/4`
`= 3/7 . 4/21 - 3/6 . 4/13`
`= 3/7 . ( 4/21 - 4/13)`
`= 3/7 . (-32/273)`
`= -32/637`