A project has an initial cost of $$7,900$ and cash inflows of $$2,100,$ $$3,140,$ $$3,800,$ and $$4,500$ per year over the next four years, respectively. What is the payback period? $3\mathrm{.}28$ years $3\mathrm{.}36$ years $3\mathrm{.}70$ years $2\mathrm{.}70$ years $2\mathrm{.}28$ years