Following a severe​ snowstorm, Ken and Bettina Reeves must clear their driveway and sidewalk.Ken can clear the snow by himself in 3 ​hours, and Bettina can clear the snow by herself in 4 hours. After Bettina has been working for 2 hours comma Ken is able to join her. How much longer will it take them working together to remove the rest of the​ snow?