You are managing the investment portfolio of a retirement plan. The expectation is to receive $50$

million USD annually $($at the end of each year$),$ during $20$ years, in some distant future. You found

an attractive infrastructure investment that yields $8\%$ annual interest and decided to deposit

$6\mathrm{.}851$ million USD every year $($including the year the retirement plan will start paying to its

beneficiaries$).$ How many years do you have to invest to get the expected return?