The Heavens Gate Group have $$43$ million in cash. In order to reach the comet that will take them to a new world they need the $$43$ million to grow to $$84$ million. How many years will it take before the group can leave if they earn $8\mathrm{.}5\%$ per annum on their stash of cash? Assume annual compounding. $($Enter your answer in years to $2$ decimal places, e$.$g$.,12\mathrm{.}34)$