Two ropes, AD and BD, are tied to a peg on the ground at point D. The other ends of the ropes are tied to points A and B on a flagpole. Angle ADC measures 60°, and angle BDC measures 30°. What is the distance between the points A and B on the flagpole?
a) 20 ft
b) 15 ft
c) 10 ft
d) 5 ft