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Example 1 of how to find the angles when lines intersect

In the figure shown, lines L1, L2 and L3 intersect at the same point. If the angle 1 is 50o, what is the value of x + y?

Note: when two lines intersect, the vertical angles are equal. A straight line forms a straight angle and the degree measure of the straight angle is 180o. Write an equation based on the equal relationship.