`a) 3/5 + (-4/3) + (-3/4)`
`= 36/60 - 80/60 - 45/60`
`= -89/60`
`b) 15/34 + 13/21 + 19/34 - 1 4/7 + 8/21`
`= ( 15/34 + 19/34) + ( 13/21 + 8/21) - 1 4/7`
`= 1 + 1 - 1 4/7`
`= 2 - 11/7`
`= 3/7`
`c) 16 2/27 : (-3/5) - 28 2/27 : (-3/5)`
`= 16 2/27 . (-5/3) - 28 2/27 . (-5/3)`
`= (-5/3) . ( 16 2/27 - 28 2/27)`
`= (-5/3) . -12`
`= 20`
`d) | -2/5| - 7 . (-6/7)^0 + (-1)^500 + 7`
`= 2/5 - 7 . 1 + 1 + 7`
`= 2/5 - 7 + 1 + 7`
`= ( 2/5 + 1 ) - ( 7 - 7)`
`= 7/5 - 0`
`= 7/5`