Answer:
As shown in picture:
BC = BA => triangle ABC is isosceles => angle BCA = angle BAC
DC = DA => triangle ADC is isosceles => angle DCA = angle DAC
=> C = BCA + DCA = BAC + DAC = A
Other wise, the sum of 4 internal angles of a quadrilateral is equal to 360 deg.
=> C + A = 360 - 100 - 45 = 215
=> C = A = 215/2 = 107.5 deg
Hope this helps!
:)
