Hi there!
As you can see, 3 and 4 both are on one side of one line. They are created by another line intersecting that same line. Now, imagine if that line wasn't there. This would make it so 3 and 4, added together, made up that one side of the line.
The measure of one side of a line is 180 degrees. Add both sides of the line together, you get a full 360 degrees circle. Thus, this means 3 and 4 add up to 180 degrees.
The definition of supplementary angles is they are a pair of angles which add up to 180 degrees. (Complementary is add up to 90, I find this easy to remember by remembering c comes earlier in the alphabet, and 90 comes earlier than 180).
Therefore, your answer is angle 3 and 4 are supplementary angles.
Hope this helps!
