xintercept is when the function equals zero since it increases only, it cannot equal zero and does not have an x intercept
after 4 years the investment value is 104 after 6 yaers value is 138.7 after 7.86 years the value is179.98 which is roughly 3 times of 60 8 years later183.54 close enough
answers f(x)=60*1.15^x after 7.86 years value is 3 times initioal value after 8 years value is 184