Consider a "professional services pyramid" like the one pictured below, and assume that the firm only does entry-level hiring (that is, all managers and partners are promoted from within). Suppose that the number of juniors, partners and managers remain relatively constant over time. New hires spend an average of 5.4 years in the "junior" ranks, considering all the modes of exit, and those who are promoted to manager spend an average of 8.0 years in that category, again considering all modes of exit. If the number of managers is constant at about 40, and only 20% of new hires are eventually promoted to manager, then how many juniors does the firm employ?