Hi there! So already noticeable, there are some given parts and pieces. AD is unknown, and BC it seems is also unknown, since they are both congruent to each other. Segment AB is twice the length of AD, and AB is parallel to BC. DC is 4 cm longer than AB.
If you've done proofs, here's one thing that can help: Angle ADC and BCD are congruent to each other by same-side interior angles theorem.
If you haven't done proofs, I'm just going to keep this a little bit more understandable. I don't want to overload you with a million formulas/theorems.
AD = BC
AB = 2(AD)
AB || BC
DC = AB + 4
Wait a minute... :)
AD x 2 = AB. AB is 4 units shorter than DC.
Try making an equation. AD can be x, AB can be y, and DC can be z.
2x = y
y + 4 = z, z - 4 = y
2x = z - 4
So try substituting in some things that can work. The length of AB has to be 2 times the length of AD. DC is AD + 4. AD can be 2, AB can be 4, and DC can be 8.
2(2) = (8 - 4)
4 = 4 :)
Looks like it works! You should probably ask your teacher/parents for help with this one, it looks a little odd. But that's the best I can do for you. :)