`c, 3/14 : 1/28 - 13/21 : 1/28 + 29/42 : 1/28 - 8`
`= 3/14 . 28 - 13/21 . 28 + 29/42 . 28 - 8`
`= 28 . (3/14 - 13/21 + 29/42) - 8`
`= 28 . 2/7 - 8`
`= 8 - 8`
`= 0`
_________________________
`d, -1 5/7 + 2/7 . (-15) + (-105) . (2/3 - 4/5 + 1/7)`
`= -12/7 + 2/7 . (-15) - 105 . (-2/15 + 1/7)`
`= -12/7 + 2/7 . (-15) - 105 . 1/105`
`= -12/7 - 30/7 - 1`
`= -6 - 1`
`= -7`