As we know when light is falling top of an object it casts the shadow at behind of the object
Here, we can see in △ABE and △CDE
∠B = ∠D & ∠E = ∠E
∴ By proportionality theorem,
$\dfrac{AB}{CD} = \dfrac{BE}{DE}$
Here, AB = ?
CD = 1.5 m
BD = 3 m
DE = 3 m
∴ $\dfrac{AB}{1.5} = \dfrac{3 + 3}{3}$
AB = $ \dfrac{6}{3} * 1.5$
AB = 3 m
∴ Height of the Lamp post is 3 m option B)