Rohit invests $ 1 every year starting from the end of the current year. If his savings earn an annual interest rate of 15%, how long will it take for him to attain a wealth of $ 20 at the end of...

Rohit invests $ 1 every year starting from the end of the current year. If his savings earn an annual interest rate of 15%, how long will it take for him to attain a wealth of $ 20 at the end of savings period?