The distance must have been sixty miles. If Sir Edwyn left at noon and
rode 15 miles an hour, he would arrive at four o'clock--an hour too
soon. If he rode 10 miles an hour, he would arrive at six o'clock--an
hour too late. But if he went at 12 miles an hour, he would reach the
castle of the wicked baron exactly at five o'clock--the time appointed.