Find the measure of an exterior angle of each regular polygon: 100-gon.

If this is a 100-gon, then not only does it have 100 sides, it also has 100 central angles.  Each one measures 360/100 = 3.6.  This is the vertex angle for each of those 100 triangles.  180 - 3.6 = 176.4, which has to be split equally between the 2 base angles.  This puts each of those at 88.2.  If you are looking for the exterior angle to each of those, it's the supplement of them. 180-88.2 = 91.8

The answer is, the streetlight is 18 inches tall.