The sum of all the exterior angles is 360 degrees..
since it is quadrilateral and the measurement for the 3 ext angles is given as 256 then you'll have the angle for the 4th as
4th exterior angle = 360-256
= 104 degrees
Remember that when you are to extend you'll have a 180-degree angle therefore the adjacent angle will be
adjacent angle = 180 - 104
= 76 degrees