Question

draw an angle of 40. copy its supplementary angle

Answer 1

The definition of supplementary angles are two angles that add up to 180 degrees. We know that a straight angle (angle that is made out of a straight line) is 180 degrees. 
So to find an angle of 40 degrees and its supplementary angle, you can draw a straight line and then measure 40 degrees from one side. Draw a line to make that angle of 40 degrees. The angle on the other side will be its supplementary angle.
Please see the image below.