It depends on the question. Is this being graphed or not? Typically “a” or any letters in algebra are an unknown value that you have to fill in for. For example, if I’m trying to figure out how many shelves I can buy for my room while staying in my budget, a possible equation for this is: $20x = $100.
$20 is the amount per shelf and $100 is my budget. You would divide $100 by 20 and see that I can buy 5 shelves.
