Sample observations of a claims processor made over a $160-$hour work month reveal that the worker produced a total of $3$ completed claims forms. The performance rating was $80\%.$ The worker was idle $20\%$ of the time $($so that idle time should: subtracted from the total time when computing the average observed time$).$ The allowance factor is ghit what is the stan per unit?

$0\mathrm{.}42$ minutes

$16\mathrm{.}0$ minutes

$17\mathrm{.}4$ minutes

$20\mathrm{.}0$ minutes

$21\mathrm{.}7$ minutes