If you count the bottom rung, the answer is 4 hours.
If the rope is 10 feet long, and each rung is 1 ft apart, there must be 9 spaces between the rungs on the ladder. This can be shown with a number line, although it is not necessary to answer the question.
One foot is 12 inches, so it would take 2 hours for one rung to be covered.
However, since we have already said the bottom rung is touching the surface of the water, it shouldn't need any inches.
So if we exclude the bottom rung, there are two rungs left. 2 x 2 = 4.
