Given :
[tex]\begin{gathered} P\text{ = \$ 1750} \\ R\text{ = 3.5 \%} \\ A\text{ = 2P} \\ A\text{ = 2}\times\text{ 1750 = \$ 3500} \end{gathered}[/tex]Amount is given as,
[tex]\begin{gathered} A\text{ = P( 1 + }\frac{R}{100})^T \\ 3500\text{ = 1750( 1 + }\frac{3.5}{100})^T \\ \text{( 1 + }\frac{3.5}{100})^T\text{ = }\frac{3500}{1720} \end{gathered}[/tex]Further,
[tex]\begin{gathered} \text{( 1 + }\frac{3.5}{100})^T\text{ = 2} \\ (\frac{103.5}{100})^T\text{ = }2 \\ (1.035)^T\text{ = 2} \end{gathered}[/tex]Taking log on both the sides,
[tex]\begin{gathered} \log (1.035)^T\text{ = log 2} \\ T\log (1.035)\text{ = log 2} \\ T\text{ = }\frac{\log \text{ 2}}{\log \text{ 1.035}} \end{gathered}[/tex]Therefore,
[tex]\begin{gathered} T\text{ = }\frac{0.3010}{0.0149} \\ T\text{ = 20.20 years }\approx\text{ 20 years} \end{gathered}[/tex]Thus the required time is 20 years.
