$10)$ A whistleblower exposed an illegal payoff scheme at a prison. The whistleblower's attorney believes his client could be eligible for a $$3$ million whistleblower pay out. The whistleblower believes this is a good start, but would need $$6$ million to retire comfortably, with the lifestyle he desires. If able to collect on the $$3$ million, how many years would it take to double his money to $$6$ million, assuming a $5\%$ discount rate? Calculate this for him using an Excel function, not with the rule of $72.($round to the nearest tenth of a year$)$