`a) ( 3/5 + ( -1)/15 ) . ( 1/2 )^3 - \sqrt{4/25}`

`= 8/15 . 1/8 - 2/5`

`= 1/15 - 2/5`

`= -5/15`

`= -1/3`

`b) (-5)/17 . 31/33 + (-5)/17 . 2/33 + 2 5/17`

`= ( -5)/17 . ( 31/33 + 2/33 ) + 5/17 + 2`

`= -5/17 . 1 + 5/17 + 2`

`= -5/17 + 5/17 + 2`

`= 2`

`c) ( 9^8 . 3 - 9^9 )/( 9^8 . 5 + 9^8 . 7)`

`= ( 9^8 . ( 3 - 9 ))/( 9^8 . ( 5 + 7 ))`

`= ( 3 - 9 )/( 5 + 7 )`

`= -6/12`

`= -1/2`