`a, (-5/11) . 7/15 . (11/{-5}) . (-30)`
`= (-5/11) . (11/{-5}) . (-30) . 7/15`
`= 1 . (-30) . 7/15`
`= -30 . 7/15`
`= -14`
_____________________
`b, (-1/3) . (-15/19) . 38/45`
`= 5/19 . 38/45`
`= 2/9`
_______________________
`c, (-5/9) . 3/11 + (-13/18) . 3/11`
`= 3/11 . [(-5/9) + (-13/18)]`
`= 3/11 . {-23}/18`
`= {-23}/66`
______________________
`d, (2 2/15 . 9/17 . 3/32) : (-3/17)`
`= (32/15 . 9/17 . 3/32) : (-3/17)`
`= (96/85 . 3/32) : (-3/17)`
`= 9/85 : {-3}/17`
`= -3/5`