Mr. Stone started from home on a trip planning to average 30 mph How fast must his son Carl plan to travel in order to overtake him in 3 hours if Carl started 1 hour after his father?

After one hour, Mr. Stone is 30 miles away from home, so he his lead over Carl is 30 miles.

In order to close the lead, Carl must cover 30 miles morethan Mr. Stone in the next 3 hours.

His speed must be (30/3) = 10 miles per hour faster than Mr. Stone's speed.

Carl must move at (30 + 10) = 40 mph.