# Trigonometry, height of mountain based on angle difference?

The text translated: From a point A on a water we observe a antenna on a mountain. The antenna is 23m high. Find the height of the mountain.

I believe the solution is in the differences between the angles. But please, only subtle hints. This is homework and I like the creative process of pondering on it myself. Right now I'm stuck. I know that sine, cos and tan is only defined for right angled triangles.
Hints people, do not just dump the answer.

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You have to make your own right angle, by continuing the line of the antenna down to sea-level. Now you can express tan $20^{\circ}$ and tan $24^{\circ}$ in terms of the sides of the two right-angled triangles, and a little algebra gives you the height of the mountain. – TonyK Aug 22 '11 at 16:48
I solved it, thanks. – Algific Aug 22 '11 at 17:52