`a)`
`-4/9 + 1/3 - (-5/6)`
`= -4/9 + 1/3 + 5/6`
` = -8/18 + 6/18 + 15/18`
` = 13/18`
`b)`
`-7/12 - (-14/15) + (-5/6)`
` = -7/12 + 14/15 - 5/6`
` = -35/60 + 56/60 - 50/60`
` = -29/60`
`c)`
`2/3 - [ -7/4 - (1/2 + 3/8)]`
` = 2/3 - (-7/4 - 1/2 - 3/8)`
`= 2/3 + 7/4 + 1/2 + 3/8`
` = 16/24 + 42/24 + 12/24 + 9/24`
` = 79/24`