tag removed – Estimate the minimum distance between his starting point and the current position

A farmer owns a rectangular farm that has a road on all four sides. He starts from one corner of the field and walks north. After going 600 meters, he takes a right turn and walks another 400 meters. Again he takes a right and walks for 100 meters Estimate the minimum distance between his starting point and the current position.

a. 360 m
b. 500 m
c. 420 m
d. None of the above

My answer came (410000)^0.5 but the answer is A. 360m