Solution: First, choose 4 distinct layers from 7, which is $ \binom74 = 35 $. Then, select 2 of these 4 layers to apply the "pump water" operation, which can be done in $ \binom42 = 6 $ ways. The remaining 2 layers are analyzed without the operation, and the sequence of 4 layers is ordered, giving $ 4! = 24 $ permutations. However, since the operation affects only the selection (not the order of non-pump layers), the total is: - Appfinity Technologies