Write a function in terms of t that represents the situation. a $900 sound system decreases in value by 9% each year.

Let cost be represented as x and time as t. If the value of the system decreases 9% each year, that means that it only retains (100 - 9)% or 91% of its value from the previous year. Based on the initial value of $900 at t = 0, this can be written as x = ($900)(0.91)^t.

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