I can't do pictures yet.Originally Posted by cinbad
Sketch this out. We've got points A and B defined. Call point C the base of the tower and D the top of the tower. You know angles DAB and DBC are 15 and 20 degrees, repsectively. Look at angle ADB. You can find that as well. So, in a nutshell, you can use the Law of Sines to find any unknown side of the triangle ABD.
I suggest side BD. The reason is that triangle BCD is a right triangle and we can figure out all the angles in it. So if we have the hypotenuse, we can find the side CD, right?