It should be 13 as well
Because the arc length of CDE and ABCD are both 90 degrees. They share 20 degrees from arc CD and they already both have 70 degrees. So if the arc length is equal, the corresponding chords should be equal too.
Congruent shapes are the same, so its safe to say that congruent shapes must also be similar.
Answer:
D
Step-by-step explanation:
So we have the expression:

Combine like terms:

Add or subtract:

Simplify:

Our answer is D