Question 1089515
{{{ F = Pe^(rt) }}}
F = Future value
P = Present value
r = annual rate expressed as a decimal
t = time in years

{{{ 28000 = 7000*e^(0.09t) }}}
{{{  4 = e^(0.09t) }}}
{{{ ln(4) = 0.09t }}}
{{{ t = ln(4)/0.09 = highlight(15.40327) }}} years  (about 15 years and 147 days)

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Check: {{{ 7000*e^(0.09*15.40327) = 7000(3.9999997) = 28000 }}}  rounded to the nearest penny.