Which angle measure below is not a possible measure of an exterior angle of a regular polygon?

45°
36°
40°
54°

All exterior angles of a regular polygon would equal 360 degrees. SO... based on that, one exterior angle would have to multiplied by whatever sum (whole number) to equal 360 degrees to find the number of sides. Here you divide 360 by one of the exterior angles, if it does not equal a whole number then it would be inaccurate.
In this case only 54 degrees would not fit into one of the exterior angles.

The operation is suck a c@ck? !