Let us start by taking Trignometric Ratios
Let us take the ratio of Tan A (where A is some angle) between the hypotenuse formed by the distance between the top point of the pole and the outer most end of the shadow of the pole. So, the ratio will be
TanA=adjacent side/ opposite side
= 6/2 root 3 =3/root3
Rationalizing the ratio
3root 3/3 = root3
Hence the angle should be 60 as Tan A=Root3=Tan60