The shadow of a city building is observed to be 100 m long. At the same time the shadow of a lamp post 9 m high is observed to be 5.5 m long. Find the altitude of the sun, and the height of the building.

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I'm thinking that since there are no angles given, the proportionality theorem of triangles will be applied. But I have doubts. So, how do you solve this?

Thanks.