9514 1404 393
Answer:
x = 3
Explanation:
The two right triangles share angle A, so the similarity statement can be written ...
ΔABC ~ ΔADE
Corresponding sides are proportional, so we have ...
BC/DE = AB/AD
x/12 = 3/(3+9)
x = 3 . . . . . . . . . . multiply by 12