How can you tell whether an exponential function models exponential growth or exponential decay?

Complete the explanation.

When the function is in the form () = , if the function models exponential growth, and if , the function models exponential decay.

Fatima plans to spend at least $15 and at most $20 dollars on sketch pads and pencils. if she buys 2 sketchpads, how many pemcils can she buy while staying in her price range? fatima can buy between and pencils. ? (type whole numbers. use ascending? order.)