You can understand this by two ways
1) through congruency rules
It says that triangle ABE is congruent to DCE
So the corresponding angles are equal
Eg
Angle A to Angle D
Angle B to angle C
Angle E to angle E
So they’re asking the angles AEB and DEC (which are equal as per congruency)
Thus you can equate them
4y-15=69
y=21
2) through vertically opposite angles
Since the triangles’ angles are vertically opposite one another, they are equal.
Then you can equate them the same way
Hope this helped!!
