Final answer:
At least 70 non-highly compensated employees must participate in the plan for it to pass the Ratio Percentage test.
Step-by-step explanation:
In order for Farrell Co.'s qualified retirement plan to pass the Ratio Percentage test, a certain percentage of the non-highly compensated employees must participate in the plan. The test requires that at least 70% of the non-highly compensated employees participate. Therefore, the answer is 70 employees (70% of 100 non-highly compensated employees).