(4/15+3/5):5/6+(11/15-8/5):5/6

`***`$\color{#1c1c1c}{\text{t}}$$\color{#363636}{\text{r}}$$\color{#4f4f4f}{\text{u}}$$\color{#696969}{\text{m}}$$\color{#828282}{\text{t}}$$\color{#9c9c9c}{\text{td}}$

`(4/15+3/5):5/6+(11/15-8/5):5/6`

`=(4/15+3/5+11/15-8/5):5/6`

`=1+(-1):5/6`
`=0:5/6`

`=0`