If we tell you that there is a relation between the numbers and letters in the given figure, can you analyze it and find the missing letter in the last box?
There's a day, that comes around once a year.
To celebrate the man, you hold dear.
He gave you life, love and will pick you up if you fall.
When it comes to guys like him, He's the best of all.
Who is he?
What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?