Given:
2.1 % loses twice a year.
So at first, the initial investment is $400.
Then first year will be,
[tex]\begin{gathered} 1.\text{ }400(1-2.1\%)=400(1-\frac{2.1}{100})=400(1-0.021) \\ 2.\text{ }400(1-0.021)^2 \end{gathered}[/tex]
Second year:
[tex]\begin{gathered} 1.\text{ }400(1-0.021)^2\times(1-0.021) \\ 2.\text{ }400(1-0.021)^3\times(1-0.021) \\ . \\ . \\ . \\ So\text{ it is }y=400(1-0.021)^{2t} \end{gathered}[/tex]
Hence, the correct option is Option D.
