#### Answer

$\frac{1}{4}$.

#### Work Step by Step

RECALL:
If a worker can finish a job in $x$ hours, then the worker completes $\frac{1}{x}$ of the job per hour.
Thus, if a job can be completed in 4 hours, then $\frac{1}{4}$ of the job gets completed each hour.
Therefore, the missing expression in the given statement is $\frac{1}{4}$.