Part A.
Since she will earn an additional $8,000 per year, then after 40 years she will have
![\text{ \$8,000}*40=\text{ \$ 320,000}](https://img.qammunity.org/2023/formulas/mathematics/college/5l9lmq1ow7k153s26jm9c852697ffp06g8.png)
So, the total amount of the additional earning is $320,000
Part B.
In this case, we need to use the compound interest formula, given by
![A=P(1+(r)/(n))^(n\cdot t)](https://img.qammunity.org/2023/formulas/mathematics/college/br9dk1xl6az1mpw36d7vdxxmeygqisc4gm.png)
where A is the future value, P is the present value, r is the annual interest rate, n is the number of compounding periods per year and t is the time. In our case,
![\begin{gathered} P=\text{ \$320,000} \\ r=0.06 \\ n=1 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/vnmbmzosu4vczky84pyphz1spmqnb1d9h2.png)
Then, by substituting these values into the formula, we have