`4 - 7/5 - 8/3`
`= 60/15 - 21/15 - 40/15`
`= -1/15`
`-1 + 1/3 - 1/9 - 1/81`
`= -81/81 + 27/81 - 9/81 - 1/81`
`= 98/81`
`4/5 - (-2/7) - 7/10`
`= 4/5 + 2/7 - 7/10`
`= 56/70 + 20/70 - 49/70`
`= 27/70`
`3/4 - [3/4- ( 16/18 + 15/18 )]`
`= 3/4 - [ 3/4- 31/18 ]`
`= 3/4 - 3/4 + 31/18`
`= 31/18`