A model predicts that the population of Springfield was 15,000 in 2005. The model also predicts that each year for the next 5 years, the population $\bm{p}$ increased by 4% of the previous year's population. Which equation best represents this model, where $\bm{x}$ is the number of years after 2005, for $\bm{x}$ $\leq$ 5?