It's a trap. The drawing is misleading. If the left triangle already has 60° and 40° then only 80° remains. Meaning there's no right angle. The vertical line should be leaning to the left slightly. The correct answer is 135°.
Wrong, as the drawing is not representative. The inner lower angle for the right triangle has to be 100°, as such the inner upper angle has to be 45° and the X angle has to be 135°.
Federation in action: 5 different people from 4 different instances correct OP, not knowing the others have done so, because federating the answers takes a minute.
To be fair I wrote the answer, then figured "surely somebody else must've written an answer by now", refreshed, saw two other answers (one 12 seconds old), thought "fuck it" and posted anyway. They're all written a bit differently so maybe some are easier to understand than others.
Good on you for admitting fault, not deleting the post, and standing strong. I know you probably feel like a total braindead fucking moron right now - and you'd be right to - which may be the only thing you've gotten right in your whole life. /s