see the attached figure to better understand the problem
we know that
in the triangle ABC
sin 30=AB/10------> AB=10*sin 30-----> AB=10*(1/2)----> 5 ft
in the triangle ABD
sin D=AB/20--------> sin D=5/20----> sin D=0.25
D=arc sin(0.25)-----> D=14.48°------> D=14.5°
the answer is the option
c. 14.5 degree
