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.