By Theorem for intersecting Chords:
AE * EC = DE * EB
AE is given as 2.5 and DE is given as 3.4.
We need to find EC.
EC = EO + OC
Since OC is the radius of the circle, it is 5.
AO is also the radius of the circle so it is equal to 5.
AO = AE + EO
5 = 2.5 + EO
EO = 2.5
EC = 5 + 2.5 = 7.5
So
AE * EC = DE * EB
2.5 * 7.5 = 3.4 * EB
EB = 5.5 (A)