A hot-air balloon is floating above a straight road. To calculate their height above the ground, the balloonists simultaneously measure the angle of depression to two consecutive mileposts on the road on the same side of the balloon. The angles of depression are found to be 17 degrees and 21 degrees. How high (in feet) is the balloon?
draw a diagram. You can see that if the height is h, then
h cot21° - h cot17° = 5280