In triangles BED and ABC,
1) ∠BED=∠BDE(BECAUSE THEY ARE CORRESPONDING ANGLES)
2)∠BCA=∠BAC(SAME REASON AS ABOVE)
∴ TRIANGLES ARE SIMILAR..
NOW,
since they are proved similar,
we can write that,
BE/BC=BD/BA
On placing the respective values...just evaluate..
12/28=x-3/2x-3
⇒x=12 units...........
