You have to prove that ΔABC and ΔCDA are congruent.
We know that ∠B and ∠D are congruent.
It is also given that AD=BC and since both segments are marked with an arrowhead, we also know that they are parallel AD||BC
Since segments AD||BC intersected by the transversal line AC, the angles formed have the following property:
∠DAC and ∠BCA are alternate interior angles, which means that they are congruent.
Line segments AC and CA are congruent by reflexive property
So,
∠B and ∠D are congruent, it is given.
∠DAC and ∠BCA are congruent because they are alternate interior angles.
Line segment AC and CA are congruent by reflexive property.
The triangles ΔABC and ΔCDA are congruent by AAS
