If $2100 is invested at the end of each year in an annuity that pays 6% compounded annually, the number of years it takes for the future value to amount to $70,000 is given by t = log 1.063. Use the change of base formula to find the number of years until the future value is $70,000. It will take approximately years for the future value to amount to $70,000. (Simplify your answer. Round up to the nearest whole number.)