Question 16379
Here's one way to do this.

If the carpenter and the apprentice can panel the room in 6 hours, then they can panel 1/6 of the room in 1 hour
But the carpenter can panel three times faster than the apprentice, so in 1 hour, they can panel 1/6 = 4/24 of the room together. Since the capenter is three timess faster the the apprentice, the carpenter can do 3/24 to the apprentice's 1/24 (1/24 + 3/24 = 4/24 = 1/6)

If the carpenter can panel 3/24 of the room in 1 hour, then it will take him/her 24/3 = 8 hours to do the entire room.
If the apprentice can do 1/24 of the room in 1 hour, then it will tkae him/her 24/1 = 24 hours to do the entire room.