$*($i$)$ Determine the expected unit cost of output, when the operator is assigned four machines.

The following data are known:

Operator rate$=$$$12\mathrm{.}00$ per hour,

Machine rate $=$$$20\mathrm{.}00$ per hour,

Average machine downtime per machine per hour $=6$ min.

Machine servicing time per unit $=12$ min,

Machine time per unit $=45$ min.

$($ii$)$ Why are performance rating and allowances considered important in stop$-$watch time study?

$($iii$)$ What approaches may be taken to overcome the problems of performance rating and allowances in industry?