Explanation:

- The cost price of all 40 items is `40x.`

- Some items are sold at the cost price of 26 items, implying their sale price is `26x.`

- The profit on these items is 30%, so their cost price is `26x / 1.3`, which equals 20 items.

- Thus, 20 items are sold at a 30% profit, and the remaining 20 items at an 18% profit.

- The profit from the first group is `20 * 0.3x = 6x.`

- The profit from the second group is `20 * 0.18x = 3.6x.`

- Total profit is `6x + 3.6x = 9.6x.`

- The overall profit percentage is `(9.6x / 40x) * 100% = 24%.`

Therefore, the correct option is:

Option 3: 24%