Explanation:

Let’s break down the problem and check each statement:

- Let cost price of 500 notebooks = Rs. 500 (assume cost per notebook = Rs. 1).

- Sold 300 notebooks for Rs. 500 ? Selling price per notebook = Rs. 500/300 = Rs. 5/3.

- Sold next 140 notebooks at 20% higher rate: Rs. (5/3) × 1.2 = Rs. 2 per notebook.

- Sold remaining 60 notebooks (500 - 300 - 140 = 60) at cost price, Rs. 1 each.

Now, let's calculate the totals:

- Selling price for 300 = 300 × Rs. 5/3 = Rs. 500

- Selling price for 140 = 140 × Rs. 2 = Rs. 280

- Selling price for 60 = 60 × Rs. 1 = Rs. 60

- Total selling price = 500 + 280 + 60 = Rs. 840

Total cost price = Rs. 500

Profit = Rs. 840 – Rs. 500 = Rs. 340

Profit percentage = (340/500) × 100% = 68%

Option 3: 68% is correct.

Option details:

- Option 1: 60% (not correct as calculated)

- Option 2: 56% (not correct, calculation mismatch)

- Option 3: 68% (? correct, matches calculation)

- Option 4: 64% (not correct, calculation mismatch)