To represent the relationship of hours worked to the amount earned using a proportion, we can set it up using the rate of pay and the total earnings. The employee makes $20 per hour, and we want to find out how many hours (x) it takes to earn $80.
The proportion can be set up as follows:
\[ \frac{20}{1} = \frac{80}{x} \]
Therefore, the correct choice is:
B. \( \frac{20}{1} = \frac{80}{x} \)