Answer
108 h
Work Step by Step
Since the number of workers needed to complete a particular job is inversely proportional to the number of hours that they work, then we have
(no. worker)(hours)=(no. worker)(hours).
That is,
$$
12\times 72=8\times x\Longrightarrow x=\frac{12\times 72}{8}=108 \ h
.$$
