A firm is evaluating a proposal which has an initial investment of $$70,000$ and has cash flows of $$20,000$

in year $1,$$$40,000$ in year $2,$ and $$20,000$ in year $3.$ The payback period of the project is

a$.2\mathrm{.}5$ years

b$.1$ year

c$.3$ years

d$.2$ years