In this question writing "sub" or 'Subject' is correct And Here in this pic before Yours - English - Formal Letter

Question

In this question writing "sub" or 'Subject' is correct ? And Here
in this pic before Yours Truly "Thanking You" is required?

Ankit Singh Jadeja · Accepted Answer

Dear Student,

Writing Subject instead of Sub is preferred However, there is
no problem in writing sub as well
It is not necessary to write Thanking you before yours
truly

Regards

In this question.. writing "sub" or 'Subject' is correct ? And Here in this pic before Yours Truly "Thanking You" is required?