It's given that AE = BE therefore triangle ABE is isoceles
That means that angle A = angle B therefore angles A + B = 114o
The total of the internal angles of a triangle is 180o therefore angle BEA = 66o
Since angle BEA is 66o then so is angle DEC because the two are vertical angles.
So angle D + angle DEC = 31o + 66o = 97o
The total of the internal angles of a triangle is 180o therefore angle C = 83o