The Vertical Angles Theorem states that vertical angles, angles that are opposite each other and formed by two intersecting straight lines, are congruent. This means that 48° should equal (7x+13)°, because they're vertical angles. The equation should appear as 48=7x+13. Subtract 13 on both sides to get. 35=7x. Divide 7 on both sides to result with x=5.
