Your calculations are a bit off, since even $75k * 0.15 * 40 = $450k (ie, not taking into account salary increases or returns).
Also, $75k is a lot more that most people make. From what I can find, that would be ~85th percentile of personal income, or around the 60th percentile of household income.
Edit: Some representative (although a bit outdated) sources:
101k a year in income, more than $2m in total balance.
Chicago police officers make $65k within 18 months [0]. If $75k is a high estimate, it’s not by a ton. Government competes for professional/managerial/educated employees as well.
Also, $75k is a lot more that most people make. From what I can find, that would be ~85th percentile of personal income, or around the 60th percentile of household income.
Edit: Some representative (although a bit outdated) sources:
https://en.wikipedia.org/wiki/Personal_income_in_the_United_...
https://en.wikipedia.org/wiki/Household_income_in_the_United...