For an initial amount P with an annually compounded interest rate r, after t years the total amount A is is given by:
[tex]A=P(1+r)^t[/tex]Then we have:
[tex]\begin{gathered} \frac{A}{P}=(1+r)^t \\ \ln\frac{A}{P}=t\ln(1+r) \\ t=\frac{\ln\frac{A}{P}}{ln(1+r)} \end{gathered}[/tex]For P = $10,000, A = $23,750 and r = 0.05, we have:
[tex]t=\frac{\ln\frac{23750}{10000}}{\ln(1+0.05)}\approx17.73\text{ years}[/tex]