Question

Two angles are supplementary. The first angle measures 40 degrees. What is the measurement of the second angle

Answer 1

Supplementary angles add up to 180º
If one is 40º, then the other is (180º-40º) = 140º

None of those choices describes a plane.
choice C is the only example of a plane.

Answer 2

two angles are supplementary so this mean adding them measure give 180 degrees 
- first angle measure 40 degree so the measure of supplement angle will be
180 -40 = 140 degrees