How do you figure out how many valence electrons an element has?

It's how many are in the element's outer layer. The layers go: 2, 8, then 8.

Ex-6 electrons. 1 layer is 2, the next layer has 4 left. If that layer holds 8, you can do 8-4 and it has 4 valence electrons.

Ex-10 electrons. 1 layer is 2, the next layer has 0 left. It has 8 valence electrons because the outermost layer is full with 8.

ex-11 electrons. 1 layer is 2, the next layer is full as well. 2+8=10; it has 1 left. So that element has only one valence electron.

The valence electron of an atom has the highest energy level and is found on the outermost energy level. It is also the group number