Alan runs to the gym at a rate a 6 mph. Then he walks home at a rate of 4 mph. IF Alan's home is d miles for the gym, how many hours does it take him to run from his home to the gym?

fist on the left goes with the third on the right. second on the left goes with the fourth on the right. third on the left goes with the second on the right. the fourth on the left goes with first on the right