Question 743001
Let d = number of days

Assuming interest is 15% per annum and that there are 365.25 days in a year  then the interest every day = 15% / 365.25.

hence {{{ (2000) (1+.15/365.25)^d = 8000 }}}

{{{ (1+.15/365.25)^d = 4. }}}


Taking logs
{{{ ln(1+.15/365.25)d = ln(4000) }}}

hence {{{ d = ln(4) / ln(1+.15/365.25) }}}

d = 3376.3198690738941804021745971694 days = 9.243 years (4 sf, using 365.25 days/year).