+37 From a certain point, the angle of elevation to the top of a church steeple is 10 degrees. At a point 100m closer to the steeple, the angle of elevation is 20 degrees. What is the height of the steeple?
+9479 
Here, DC is the height of the steeple.
The angle next to angle B = 180º - 20º = 160º
So the remaining angle in that triangle = 180º - 160º - 10º = 10º
So this is an isocolese triangle. (I just spent about 10 minutes typing an answer before I realized this....sighh...)
That means that AB = BD.
BD = 100 m
sin = opposite / hypotenuse
sin 20º = DC / 100
100sin20º = DC
34.202 meters ≈ DC
