Explanation:

- Combined work of P, Q, and R: They finish the work in 16(4/11) days. This is equivalent to 180/11 days. Their combined work rate is 11/180 of the work per day.

- P and Q together: They can complete the same work in 20 days. Hence, their combined work rate is 1/20 of the work per day.

- Work rate of R alone: The work rate of P, Q, and R minus the work rate of P and Q gives R's rate. So, R's rate is \(11/180 - 1/20\).

- Simplifying R's rate: \(11/180 - 9/180 = 2/180\), which simplifies to 1/90 of the work per day.

- 60% of the work: If R works alone, it will take \(1/90\) days per unit. So, for 60% of the work, it takes \(0.6 \times 90 = 54\) days.

Answer: Option 3: 54 days

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