Let x be the amount of 18% sulfuric acid that needs to be added.

The amount of sulfuric acid in 360 mL of a 10% solution is:

360 mL x (10/100) = 36 mL

The amount of sulfuric acid in the final 15% solution will be:

(36 mL + x)

Step 2: Set up the equation

According to the question, the final solution should have a concentration of 15%. Therefore, we can set up the following equation:

(36 mL + x) / (360 mL + x) = 15 / 100

Step 3: Solve for x

Cross-multiplying and simplifying the equation, we get:

100 (36 mL + x) = 15 (360 mL + x)

3600 mL + 100x = 5400 mL + 15x

85x = 5400 mL - 3600 mL

85x = 1800 mL

x = 1800 mL / 85

Therefore, 21.2 mL of 18% sulfuric acid should be added to 360 mL of a 10% solution to obtain a 15% solution.