Today is $\frac{1}{7}\frac{?}{2021},$ John plans to deposit $$500$ at the beginning of each month into an investment fund. The first deposit will be deposited today. John predicts that the return rate of this

fund will be $j_2=3\mathrm{.}51\%$ from $\frac{1}{7}\frac{?}{2021}$ to $\frac{30}{9}\frac{?}{2021}$ and $j_2=4\mathrm{.}98\%$ from $\frac{1}{10}\frac{?}{2021}$ to $\frac{31}{12}\frac{?}{2021}.$ What will be balance amount of this account on $\frac{31}{12}\frac{?}{2021}?$ Round your answer

to three decimal places.

a$.3041\mathrm{.}113$

b$.3039\mathrm{.}753$

c$.3039\mathrm{.}232$

d$.3040\mathrm{.}139$