The purchasing power $P($in dollars$)$ of an annual amount of A dollars after $t$ years of $3\mathrm{.}1\%$ inflation $($the rate of inflation for November $2023,$ according to the U$.$S$.$ Labor Department$)$ decays according to the following formula:

$P=A{e}^{-0\mathrm{.}031t}$

How long will it be before a retirement pension of $$90,000$ per year has a purchasing power of $$20,000?($Round your answer to two decimal places.$)$ Write $1-2$ sentences on what this means to you without using the phrase "purchasing power."