Answer:x = 8Step-by-step explanation:If the line are parallel (those are the ones that dont cross) and a third line crosses both the parallel lines, you get the set up shown in your diagram. Which has EIGHT angles in it. But there's only two measures for all eight of these angles. Four of them are all equal to each other (and the other four all equal to each other) And the two numbers add up to 180° Here 7x + 12 and 12x - 28 are a couple of the angles that are EQUAL TO each other.7x + 12 = 12x - 28 Solve.Subtract 7x from both sides.12 = 5x - 28 add 28 to both sides.40 = 5x divide by 5 on both sides.40/5 = x8 = x