An investment project provides cash inflows of $$645$ per year for eight years.

a$.$

What is the project payback period if the initial cost is $$1,800?($Enter $0$ if the project never pays back. Do not round intermediate calculations and round your answer to $2$ decimal places, e$.$g$.,32\mathrm{.}16.)$

b$.$ What is the project payback period if the initial cost is $$3,500?($Enter $0$ if the project never pays back. Do not round intermediate calculations and round your answer to $2$ decimal places, e$.$g$.,32\mathrm{.}16.)$

c$.$ What is the project payback period if the initial cost is $$5,300?($Enter $0$ if the project never pays back. Do not round intermediate calculations and round your answer to $2$ decimal places, e$.$g$.,32\mathrm{.}16.)$