These parallel lines cross 1 line. Because they are parallel they will form the same angles on that line. Therefore, x+50 = 3x-100 since those angles are corresponding angles made by a pair of parallels.
To find x we need to find what value of x gives the same answer for 3x-100 and x+50 since those 2 angles are equal.
x+50 = 3x-100 - now all we need to do is solve for x:
