What is the measure of an exterior angle of a regular quadrilateral

-- Any "regular" polygon has all sides equal AND all angles equal.

-- The sum of the angles inside a 4-sided figure is 360° .

-- So it it's a regular figure, then each angle is 360°/4 = 90° .

-- The total angle around each vertex is 360° .
If 90° of them are inside, then the exterior angle is the remaining 270° .

45 this is because of the agarose