Correct Answer - Option 3 : 10000

**Calculation:**

Let the number of pages to be printed be x

When total cost incurred on both the types of printers is equal,

⇒ 5000 + 1.8x = 8000 + 1.5x

⇒ x = 10000

**∴ No. of pages have to be 10,000**

Here, using the first machine, we can print more pages for the same overall cost incurred. Hence, the first machine shall be more useful when the number of pages to be printed is 10,000.