Hello!
The answer is:
The telephone pole is 20.8 foot tall.
Why?
Since it's not mentioned, we can assume that both, man and the telephone pole are close, so, if two similar triangles are created, we know that both shadows are proportional and we can find the telephone pole height creating a proportionality relationship.
We can find the telephone pole height using the following equation,

Were,
Man height is 6 foot
Man shadow is 4.5 feet long
Telephone pole shadow is 15.6 feet long.
So, substituting we have:


So, the telephone pole is 20.8 foot tall.
Have a nice day!