From the information given, segments AB and NM are the diameters of the circle. They are straight lines.
Recall, the angles formed on a straight line are called linear pairs and their sum is 180 degrees. This means that the sum of the angles on segment NM is 180 degrees. Thus,
angleMEA + angle AEC + angle CEN = 180
From the diagram,
angle MEA = 55
angle CEN = 65
Thus,
55 + angle AEC + 65 = 180
120 + angle AEC = 180
angle AEC = 180 - 120 = 60 degrees
Now, we would consider segment AB. It means that
angle AEC + angle CEN + angle BEN = 180
By substituting the values, we have
60 + 65 + angle BEN = 180
125 + angle BEN = 180
subtracting 125 from both sides, we have
angle BEN = 180 - 125
angle BEN = 55 degrees