The idea from Emile is the correct one. Have a look at an ASCII tabe (for instance http://asciichart.com). From A to Z are the numbers 65 to 90. Chr(65) = A and so on. Then you need to do an integer division of 26 to get the number of letters. Can you now get the algorithm?
You could also use a constant with each of the letters in it and then use the modulus operator for the position and integer divisor \ to get the count.
b. For the Row #, you may add a second Listbox with only one column and fill the Column in a Loop, and synch the two Listbox scroll.
If you add or remove a Row, you can populate the Listbox.