An investment project has annual cash inflows of $$4,200,$$$5,100,$$$6,300,$ and $$5,500,$ for the next four years, respectively. The discount rate is $15$ percent.

a$.$ What is the discounted payback period for these cash flows if the initial cost is $$6,900?($Do not round intermediate calculations and round your answer to $2$ decimal places, e$.$g$.,32\mathrm{.}16.)$

b$.$ What is the discounted payback period for these cast flows if the initial cost is $$9,000?($Do not round intermediate calculations and round your answer to $2$ decimal places, e$.$g$.,32\mathrm{.}16.)$

c$.$ What is the discounted payback period for these cash flows if the initial cost is $$12,000?($Do not round intermediate calculations and round your answer to $2$ decimal places, e$.$g$.,32\mathrm{.}16.)$