To find the rate of change of temperature per hour, we need to determine the derivative of the temperature equation $T(t) = 5t + 20$ with respect to time $t$.

The derivative of $T(t)$ with respect to $t$ is:

$\frac{dT}{dt} = 5$

This represents the rate of change of temperature per hour.

Thus, the rate of change of temperature is 5°C per hour.

The correct answer is A) 5°C per hour.

Would you like more details or have any questions? Here are some related questions for you:

1. How do derivatives relate to rates of change?
2. What is the physical significance of the slope of a linear equation?
3. Can the rate of change be negative in certain cases?
4. How would you calculate the rate of change for a non-linear equation?
5. What is the unit of measurement for a rate of change?

Tip: In many real-world scenarios, the rate of change is represented by the slope of the function.