As we can see n the diagram, there are parallel traversals and one line, and the two angles given are same-side interior angles. We know that when there is parallel traversal, and we have same side interiors, the sum of the measure of the two angles are supplementary. Supplementary means 180 degrees, or a straight line.
So we plug everything in and we have 4x+5x=180 degrees
4x+5x=9x, so 9x=180
We divide by 9 on both sides to get the value of x, which is 20
