How to Understand the rule of vertically opposite angles

In this video we learn how to understand the Rule of Vertically Opposite Angles. This says that when two straight lines cross it produces vertically crossed lines that must have congruent angles. Because the lines are straight this has to happen. Remembering the rule "supplementary" you will be able to calculate the angle of A and B in the equation. Prove what each of the angles are using the different rules and then move onto the other two angles. Angle C can be figured out by knowing that it's equal to angle B with the vertically opposite rule. Once you understand these rules, you will be able to figure out these equations!