The mean of a dataset is simply the sum of the elements, divided by how many elements you have.
In your case, you have a dataset of 10 elements, so we will divide by 10.
The sum of the elements is
![5+8+9+11+7+7+8+9+12+7=83](https://img.qammunity.org/2020/formulas/mathematics/high-school/jisw73css8vxlc3yk0wexxhvk7g7qb6s4w.png)
Which implies that the average is
![(83)/(10)=8.3](https://img.qammunity.org/2020/formulas/mathematics/high-school/zrk3h1h8fjq4dz1gecknmhu5cvwm82klf8.png)
Which should be approximated to 8.