### Example 1 of how to find the angles when lines intersect

In the figure shown, lines L_{1}, L_{2} and L_{3} intersect at the same point. If the angle 1 is 50^{o}, 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 180^{o}. Write an equation based on the equal relationship.