Gates, a full$-$time student, is faced with a computer purchase decision. The cost of a new personal computer is $$2,000$ and Gates estimates that he would save $$400$ per year by paying someone else to have his term papers typewritten. The payback period for this decision is

$\mathrm{.}20$ or $20$ percent of a year.

five years.

$$800,000$ in $10$ years.

unable to be calculated, based on the information given.