What should be placed instead of the question mark?
The “Y” means a “year”. The pockets are the collections of months starting with the same letter. The letter in each pocket stands for the first letter of a month, the digit – how many such months are in a year. There 5 unique months in a year starting with one letter: February, September, October, November and December. There are two couples of the same start-letter months: March and May; and April and August. There are three months starting with the same letter: January, June and July.