Answer:
? = 7.
Step-by-step explanation:
The two triangles are similar because of the AA Theorem.
The larger triangle's side that is equal to 9 + 3 corresponds to the smaller triangle's side length of 9, while the larger triangle's 21 + ? side corresponds to the smaller triangle's 21 side. Now, we can set up a proportion!
? + 21 = 7 * 4
? + 21 = 28
? = 28 - 21
? = 7
Hope this helps!