PLEASE EXPLAIN HOW ALL CALCULATIONS WERE MADE IN DETAIL

I've seen other posts on this but they aren't too clear and are hard to follow what calculation supports what part of the question. Thank you!

$3)$ Using the analysis performed in $(2),$ prepare $$best$$ and $$worst$$ case scenarios using the following assumptions:

a$)$ Best Case $$ Projected sales expectations increase by $10\%,$ required rate of return falls to $7\%.$

b$)$ Worst Case $$ Projected sales decreases by $10\%,$ required rate of return increases to $15\%.$

$4)$ Write a memo to the CFO of IEC providing your analysis and recommendation regarding the

PPDs$.$ Be sure to compare your results to the competing proposal. Include a strong recommendation for or against the acceptance of the new PPDs into IEC$$s product line.

$$