What is the payback period for an investment with these cash flows: YR $0,-60,000$; YR$1,10,000$; YR $2,20,000$; YR $3,15,000$; YR $4,20,000$; YR $5,15,000?1\mathrm{.}75$ years$2\mathrm{.}75$ years$3\mathrm{.}75$ years$4\mathrm{.}00$ years$4\mathrm{.}75$ years