We have the following:
The domain is the input values or also the x-axis values.
According to the graph we can see that we go from 0 to 8.
Because the point at 0 is filled, it means that it includes the number and that means that it is a closed interval [].
On the contrary, at point 8, the point is hollow, it means that it reaches 8, but it does not include the number 8, which means that it is an open interval ().
Which means that the correct answer is:
[0, 8)