Solutions; Let AE = X.

If AB=25km and AE=X, then BE = 25-X..

Because AD= 15km, BC= 10km, DA is perpendicular to AB and CB is perpendicular to AB.

So according to Pythagorean theorem, DE 2 =15 2+x 2, BC 2 =10 2+(25-x) 2.

Because DE=EC, x =15 2+x2 =10 2+(25-x) 2 solution.

That is, AE= 10km= 10000m.