Note that we are given two triangles that have one side in common. Also we are told that the other sides are paired into two pairs of congruent sides. Note that as segment AC is congruent with itself, we actually have three pairs of congruent sides.
By the SSS postulate (Side -Side - Side) two triangles that have three pairs of congruent sides are congruent.
So it follows that both triangles are congruent