Question

Picking a month of the year in the day of the week (fundamental counting principle)

Answer 1

Since you mentioned the fundamental counting principle, I assume you are looking for the total number of possibilities.

If you are picking a month, there are 12 options.
If you are selecting a day of the week, there are 7 options.

If you are doing both, you multiply the two numbers together.
12 x 7 = 84