How long will it take for water to hit his house?

Question

A man built his house above a river between two trees. He attaches his house to the middle of the two tree's trunks. He does this because the river rises by 2 inches each years, but the trees grow 1 inch each year. If his house is 4 inches above the river how long will it take for water to hit his house?

Answer 1

Each year, the river rises by 2 inches and tree grows by 1 inch,
so the relative gap between river level and house gets decreases by 1 inch every year.

So, the gap of 4 inches will be covered in 4 years, and then water will hit the house.