-- We're pretty sure that this question is based on an assumption of EARTH, so we know that we're dealing with a sphere of roughly 3.950 miles radius.
-- The distance on the sphere between 30° west and 60° east is 90° of longitude. That's 1/4 of the total circumference of the circle.
-- BUT ..... Way up here at 60° N latitude, the circle is not as big as the equator. It's radius/diameter/circumference is only cos(60°) = 0.5 of the Earth's total.
-- So the length of our quarter-circle arc is about
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