Final answer:
The function rule for the relationship between the amount of plant food remaining and the number of days that have passed is f(x) = (x+5)^2.
Step-by-step explanation:
The function f(x) represents the relationship between the amount of plant food remaining and the number of days that have passed. The correct function rule for this relationship is d) f(x) = (x+5)^2. This function represents the amount of plant food remaining as a function of the number of days that have passed. The function is quadratic, with the variable x representing the number of days and (x+5)^2 representing the amount of plant food remaining.