The reason we are looking for is Side-Side-Side, which means that, to prove they are congruent using this reason, we need to prove that each corresponding sides of the two triangles are congruent.
In the picture, the red marks indicate that the sides RQ and SD are congruent, so this is given.
Also, side QS is share by the triangles, which means this is aready a congruent side.
The missing sides, RS and QD, need to be proven congruent for us to complete the reason Side-Side-Side.
So, the additional information needed is:
