Angle PJK and Angle DJB are vertical angles. They are formed when you cross PD and KB. They are opposite one another. Vertical angles are congruent, so,
(angle PJK) = (angle DJB) 3x-40 = 2x-10 3x-40-2x = 2x-10-2x ... subtract 2x from both sides x-40 = -10 x-40+40 = -10+40 .... add 40 to both sides x = 30
Side Note: if x = 30, then angle PJK is... angle PJK = 3x-40 angle PJK = 3*x-40 angle PJK = 3*30-40 angle PJK = 90-40 angle PJK = 50 degrees which is also the measure of angle DJB
