**Answer:** ** O**

**Explanation:**

Working in rows, from left to right, in the top row add 3 to the numerical value of the first letter to give the next one along, then 4,then 5. In the next row, add 5 to the first letter, then 6, then 7. In the third row, start by adding 7, then 8, then 9, and in the bottom row, add 9, then 10, then 11.