Explanation:

- The shopkeeper's cost price for the notebook is Rs85.

- Desired profit is 20%, so selling price should be Rs85 + 20% of Rs85 = Rs102.

- A discount of 15% is given on the marked price.

- Let the marked price be 'x'. After a 15% discount, the selling price is 85% of 'x' (0.85x).

- Set 0.85x equal to the required selling price for a 20% profit, Rs102.

- Solve 0.85x = 102 to find x, the marked price.

- x = 102 / 0.85 = Rs120.

Option 4: Rs120 is the correct price at which the notebook should be marked.