Did you find box 12?
Because boxes 12,13,14 can have more than one row.
..
...........the first row showing is just given the added letter when it's needed to identify which "exact" box is being referred to.
Thus 12a,13a,14a refers to the first row of boxes 12,13,14
....and if you happen to need a second row (most people don't), then those will be 12b,13b,14b
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
