Answer:
I agree that this question can be confusing:
Apparently point A and point B must be on the same straight line (measured from the light house or the question would be nonsensical)
tan 13 = H / DA where H is height of lighthouse
tan 8 = H / DB tangent measured from point B
tan 13 / tan 8 = DB / DA
DB = .2309 / .1405 * 1279 = 2101 ft
DB - DA = 2101 - 1279 = 822.0 ft