b$.$ If each shift has $100$ workers, the productivity of an individual worker is $100$ workers $/20$ working hours per shift.

The productivity of an individual worker is calculated by dividing the number of workers on each shift by the number of working hours per shift. In this case, the productivity of an individual worker is $100$ workers $/20$ working hours per shift, which is $5$ parts$/$hour$.$

c$.$ To calculate the multifactor productivity of the plant from part A$,$ we need to consider the capital costs, labour costs, and production costs. The production cost per part is the material cost plus the capital cost, which is given as $$(10)/$part$.$

Multifactor productivity $=$ Total output $/$ Total input cost

Multifactor productivity $=100,000$ parts $/(100000+$

$10)$

Multifactor productivity $=100,000$ parts $/$ $$110,000$

Multifactor productivity $=0\mathrm{.}92$ parts$/$hour