Giúp em nhà súbsbsibsbsjsjshshsis

`a,`

`3 1/4 - 5/(-6)`

`= 13/4 + 5/6`

`= 39/12 + 10/12`

`= 49/12`

`b,`

`-7/12 + 4/15`

`= -105/180 + 48/180`

`= -57/180`

`= -19/60`

`c,`

`13/15 - 4/7 + 3/15 - 3/7`

`=(13/15 + 2/15) + (-4/7 - 3/7)`

`= 1 + (-1)`

`=0`

`d,`

`7/9 + 2/9 . 3/4`

`=7/9 + 1/6`

`= 28/36 + 6/36`

`=34/36`

`= 17/18`.