Make each panel have a letter value as "string" variable. Assuming you have a field (textbox) to enter the letter, then a button to check for matches. Use for each.
On button click use "for each" to check panel variable equals textbox variable. If true change animation to reveal letter.
If not do nothing or play sound.
Try to work it out. If you need a written example post back and I'll create a more visual outline.
Hope this helps. Good Luck.