To help you find the growth rate at $t = 20$, I need more context about the problem. Typically, a growth rate is represented as the derivative of a function describing growth over time. This function could be:

1. Exponential growth (e.g., population growth, compound interest): $f(t) = P e^{rt}$
2. Logistic growth: $f(t) = \frac{L}{1 + e^{-k(t-t_0)}}$
3. Linear growth: $f(t) = mt + b$
4. Any other specific growth model.

Please provide the equation or function that describes the growth, and I can calculate its rate at $t = 20$. Alternatively, if the growth is based on a table or data points, share that information.

Would you like to provide more details or an equation?

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Here are five related questions for deeper understanding:

1. Are you working with an exponential or logistic growth model?
2. Is the function modeling population growth, investment, or another process?
3. Do you need the growth rate using derivatives?
4. What units are associated with $t$ (time)?
5. Do you need a specific method for calculating the rate?

Tip: The growth rate is often linked to the derivative of the function describing the change over time.