First you find your average speed from your trip from Orlando to Miami. Since you traveled 240 miles in 4 hours, you divide 240 ÷ 4 to get 60 miles per hour (mph).
Then you use that rate for your trip from Ft. Lauderdale to Tallahassee. Since you are now traveling 420 miles, at a rate of 60 miles per hour, you divide 420 ÷ 60 to get 7 hours.