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Which of those sequences is a geometric sequence

An architect is designing a water fountain for a park she uses the given function to model the water jet flowing from the fountain nozzles where h(x) gives the height of the water jugs in feet x feet from the starting point h(x)=-1/20x+x+15

What is the best way to answer questions with a x expression in the question. for example 3x + 10x=?