I'm not sure if I'm asking this correctly, so please help me clarify if needed!

first example:
=SUM(AI49:AN49)-SUM(AI48:AN48) in which "AN" is regularly extended (AO, AP,
etc.).
How can I create a formula that gives me an answer when cell 49 is standard
and cell 48 is continuously updating? Currently, I am manually changing "AN"
to "AO", and so on as I update the information.

second example:
=SUM(AI48:AN48)/SUM(AI49:AN49) with the same situation as above.