The correct answer is - 11.
According to the diagram, in Virginia can be found fossils from 11 geologic periods. That can easily be seen on the graph and the legend bellow it. The legend tells us which period is marked with which color. There's 11 periods on the legend, thus 11 different colors, and on the graph they are all represented, some more some less, but they are there.
This means that in Virginia can be found fossils from all sorts of marine life and terrestrial life from the present back two few hundred million years ago.