Answer: the eastbound train had travelled 12 miles Explanation: using Pythagoras theorem, we know that X^2 = a^2 + b^2 Where ^ stands for raised to power. Let a stand for the train going towards North and b stands for the train going towards east. X stands for the total distance between train a and b = 20 miles. By Pythagoras rule X^2 = a^2 + b^2 20^2 = 16^2 + b^2 400 = 256 + b^2 so that b^2 = 400 - 256 = 144 b = √144 b = 12 miles.