6. What is the name of the symbol A? What does this symbol mean when
used before another symbol in an
equation?

"at symbol"

The at sign, "at symbol", is normally read aloud as "at"; it is also commonly called the at symbol or commercial at. It is used as an accounting and invoice abbreviation meaning "at a rate of" (e.g. 7 widgets "at symbol" £2 per widget = £14), but it is now seen more widely in email addresses and social media platform handles.