If the upper triangle has a right angle at Island C, we need only use the Pythagorean Theorem to find x:
(10 mi)^2 + (20 mi)^2 = x^2, so that
x^2 = 100 mi^2 + 400 mi^2 = 500 mi^2, which reduces to
x = +10√5 mi
Note that the shortest side (10 mi) is adjacent to a 30 degree angle. Thus, the upper triangle is a 30-60-90 triangle, meaning that the Pythagorean Theorem DOES apply here.
Next time, please incude ALL of the verbal instructions. Thank you.
