A bucket is being lifted to 20 ft in the air and starts with off 16lbs of water and is leaking at a constant rate. It finishes draining just as it reaches the top. How much work was spent lifting the water alone? (find the proportion of water left at elevation x ft)

the answer is 160 lbs ft but I got 3200

3200/4= 160 but I don't see how that would fit from the given information