Is an exterior angle of a quadrilateral is 90 degrees is sometimes, always, or never true

An exterior angle of a quadrilateral not will be never of measure of 90 degrees bc. the interior angles of a quadrilateral has measure of 90 degrees  

I'm not sure exactly but my best guess would be 1/4

This is what i found “an explicit formula designates the nth term of the sequence, as an expression of n (where n = the term's location). it defines the sequence as a formula in terms of n. this example is an arithmetic sequence(the same number, 5, is added to each term to get to the next term).” i hope this you for what your looking for. can you plz mark me brainliest?