https://mindyourdecisions.com/blog/2016/09/04/the-hardest-easy-geometry-problem-sunday-puzzle/ Refer this link for problem diagram
We can formulate a system of 4 equations involving angles CEF, AFE, AEF, BEF, and specify ranges for each angle (greater than 0, less than 180), using this we can get new ranges for each angle between which we can choose any value for one of these angles and put it in these 4 equations and get the values of other 3, which means that x is not unique.
If you search for this question, others have used unnecessary derivations to prove x is 30 degrees (which in my case is one of the infinite solutions)
Edit: only angles unknown in this figure are: AEF, AFE, CFE, BEF (Which is x) Now below equations can be easily derived:
BEF + CFE = 110,
AFE + AEF = 160,
AFE + CFE = 130,
BEF + AEF = 140
Now for angles to remain in range 0-180, below conditions must be satisfied:
0 < BEF < 110,
0 < CFE < 110,
30 < AEF < 140,
20 < AFE < 130
Now choose value of any one angle in above range and use above equations to find the values of other three.
(BEF=30 is one of the infinite solutions)