Working with laws and of sines and cosines.
two observers are standing on shore 1/2 mile apart at points a and b and measure the angle to a sailboat at a point c at the same time. angle a is 63 degrees and angle b is 56 degrees. find the distance from each observer to the sailboat.

Given that:
A = 63
B = 56 
C = 61 (since these angles should be equal to 180)

a = 
b =
c = 1/2

sin 63 / a = sin 61 / .5
a = .51 miles

sin 56 / b = sin 61 / .5 
b = .47 miles 

The correct answers are: 0.51 miles and 0.47 miles. These are the distances from each observer to the sailboat. 

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