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.
