Answer: 8 hours
Step-by-step explanation:
Let x be the time taken by each person to paint the fence.
Given: Tom and Becky can paint Jim's fence together in 12 hours.
Since all people paint at the same rate, then we have the following equation ;-
Thus, the time taken by each person to paint the fence alone = 24 hours
Now, the time taken by all three paint together:-
Hence, it would take 8 hours if all three paint together.