From point C, an observer on a yacht measures the angle of elevation of point D at the top of a cliff to be 25 degrees. At this point the bearing of the cliff from the yacht is 300 degrees. After the yacht has sailed 100 m on a fixed course to pt A, the cliff is due north of the observer and the angle of elevation to the top of the cliff is 15 degrees. Point B is vertically below D at the base of the cliff.
a) Show that angle ABC = 60 degrees.
b) Show that BC = BDtan65 and that AB = BDtan75
c) Calculatethe height of the cliff.
I've done parts a + b. Could someone show me how to do c). The answer is 31 m but I can't seem to get it. I used Pythagoras' Theorem.