The equation \( f(t) = 400 \cdot 1.15^t \) represents a scenario where a quantity starts at 400 and increases by a factor of 1.15 for each time period \( t \). The factor 1.15 indicates that the growth rate is 15%.
Given the options provided, the scenario that best represents this equation is:
A population of birds starts at 400 and has an annual growth rate of 15%.
This is because the population starts at 400 and grows by 15% each period (assuming \( t \) is measured in years). The other options do not align correctly with the growth indicated by the equation.