a, `5/15 + 14/25 - 4/3 + 11/15`

`= (1/3 - 4/3) + (14/25 + 16/15) `

`= -1 + (210/375 + 400/375)`

`= -1 + 610/375`

`= -1 + 122/75`

`= 7/75`

``

b, `5/10 + 1 7/11 - 25% - (18/11 - 4/9)`

` =1/2 + 18/11 - 1/4 - (18/11 - 4/9) `

`= 1/2 - 1/4 + (18/11 - 18/11) + 4/9 `

`= 1/4 + 4/9 `

`= 13/36`

``

c, `-3/4 . (-12/5) . (-25/6)`

`  = (31225) / (456)`

`= (335) / 2 `

`= 45/2`

``

d, `2 1/9 . 2/3 + 15 8/9 . 2/3`

`=19/9 * 2/3 + 143/9 * 2/3`

`= (19/9 + 143/9) * 2/3`

`= 162/9 * 2/3`

`= 18 * 2/3 `

`= 12`