$4)$ You deposit $$5,000$ into a savings account. $15$ months later later, you deposit another $$2,500.18$

months after that, you deposit $$3,000.$

The account earns interest at a nominal rate of $6\%$ compounded quarterly for the first two years.

After that, the nominal rate increases to $8\%,$ still compounded quarterly. $5$ points

a$)$ How much is in the account at the end of $4$ years?

b$)$ What is the equivalent annual effective interest rate earned