`a) 4/10 + 3/5`

`= 4/10 + 6/10`

`= (4 + 6)/10`

`= 10/10 = 1`

`b) 11/2 - 3`

`= 11/2 - 6/2`

`= (11 - 6)/2`

`= 5/2`

`c) 2/3 xx 3/4`

`= (2 xx 3)/(3 xx 4)`

`= 2/4`

`= 1/2`

`d) 4/15 : 2/5 + 7`

`= 4/15 xx 5/2 + 7`

`= (4 xx 5)/(15 xx 2) + 7`

`= 2/3 + 7`

`= 2/3 + 21/3`

`= (2 + 21)/3`

`= 23/3`