How to do missing vertical angles?

You don't "do" vertical angles, any more than you "do" triangles, fractions,

or arithmetic problems.

In order to answer a question or solve a problem, you must first understand

very clearly what the question is. In math, the question is almost always to

calculate or identify some unknown quantity. The way to "do" that is to take

the given information, then use what is known, together with all the rules and

procedures you know about the relevant operations, functions, or figures, to

find what is unknown.