Pre Calc

The formula:  A  =  P·e^r·t

A is the final amount     $2400

P is the principal           $1200

r is the rate                      0.08

y is the number of years

A  =  P·e^r·t                             --->     2400  =  1200·e^{0.08 · t}

Divide both sides by 1200     --->    2  =  e^{0.08 · t}

Take the ln of both sides:      --->    ln(2)  =  ln( e^{0.08 · t} )

Property of logs:                   --->    ln(2)  =  t ·ln( e^0.08 )

Property of logs:                   --->    ln(2)  =  t · 0.08

Divide:                                  --->   t  =  ln(2) / 0.08  =  8.66434

This is years, you will need to switch into years and days ...

Nice, Geno!