Final answer:
To find the rate of change of brightness at time t = 4 days, more specific information is needed.
Step-by-step explanation:
To find the rate of change of brightness at time t = 4 days, we need more specific information about the situation in question. The rate of change of brightness can depend on various factors, such as the intensity of the light source, the distance from the light source, and any intervening objects that may affect the light. Without more details, it is not possible to provide a specific calculation for the rate of change of brightness at t = 4 days.