You can think of this question like the photos attached above.
Also, a friendly reminder (I am sure that you know this already though) that variables cannot be capital letters (only lowercase). I used to make (and still make) this mistake a lot when writing equations, so I just thought that this reminder might be helpful.
Because this shape is a quadrilateral, so the sum of the angles of a quadrilateral is a total of 360 degrees. So i added 90 + 90 + 64 = 244. And 360 - 244 = 116.