The numerical value (position) of the letters A to Z is from 1 to 26 respectively. Considering each column from left to right, we have the total numerical value of the letters in the following column one unit higher than the previous column. The total numerical value of the first column letters is: 1 + 7 + 3 + 6 = 17 (where A = 1, G = 7, C = 3, F = 6). Similarly, we can calculate the total numerical value of the letters in the second and third columns to be 18 and 19 respectively. According to this rule, the total number value of the last column is 20, and this column has only one cell. It follows that the letter to be filled in this column has a numerical value in the alphabet of 20. That's the letter T.
