NEED HELP WITH PART B and C$.$

The following are the cash flows you expect to receive for two different investments you could make with the $$4,000$ that you saved last summer:

Alternative $1$ is $6$ years and the cash flows are given below:

$\backslash$table$[[$Year$,0,1,2,3,4,5,6],[$Cash flow,$-3,500,1,000,1,000,1,000,750,750,2,750]]$

Alternative $2$ is $8$ years and the cash flows are as follows:

$\backslash$table$[[$Year$,0,1,2,3,4,5,6,7,8],[$Cash flow,$-4,000,1,200,1,200,1,,00,1,200,1,200,600,600,3,200]]$

a$)$ What is the internal rate of return of A and B$.$ Hint: Use Excel @IRR function and attach a screenshot of your work. Solution: IIR $($Alt $1)=21\mathrm{.}92\%$ IIR $($Alt $2)=25\mathrm{.}41\%.$

b$)$ How can we be sure that there are NO more IRRs than the ones found in part a$)$

c$)$ What is the internal rate of return of the incremental cash flows associated with "stepping up$"$ from alternative $1$ to alternative $2?$ Include the incremental cash flows in your solution. Solution: $48\mathrm{.}61\%$