Explanation:

Let’s break this down:

- Layers are commercial egg-laying hens. "Economical" here means they produce enough eggs to cover feed and care costs, bringing profit.

- Typically, layers are productive starting around 18-20 weeks of age.

- Their best, most profitable laying period runs up to about 72-80 weeks of age. That’s around 15-18 months on average.

- Past this age, the rate of laying drops, feed costs stay high, and profits dip—so farmers usually cull or sell them.

- Let’s look at your options:

- Option 1 (12 months): Too short. Most hens are only just reaching peak laying.

- Option 2 (36 months): Too long. Not profitable—production falls off well before this.

- Option 3 (18 months): This is the sweet spot. Hens are productive and economical up to about 18 months.

- Option 4 (15 months): Also close, and within the range, but 18 months is more accurate.

- Option 5 (10 months): Way too early; layers haven’t reached full output yet.

So, the correct answer is Option 3: 18 months.