B starts 4 minutes after A from the same point, for a place at a distance of 7 miles from the starting point. A on reaching the destination…

B starts 4 minutes after A from the same point, for a place at a distance of 7 miles from the starting point. A on reaching the destination turns back and
walks a mile where he meets B. If A's speed is a mile in 8 minutes then B's speed is a mile in ____ minutes