Divide values ​​in one column by values ​​in another in PostgreSQL How to do?

Question

PostgreSQL

There are a bunch of tables in the database, by accessing the necessary tables through SELECT and JOIN we get the sum of the required values ​​(we designate the new row as A), we do the same for the second column (we designate it as B). What do we end up with? We have two tables A and B in which certain values ​​\u200b\u200bare obtained during the calculation when referring to other tables.
So the question is how to divide the values ​​in table A by the values ​​in table B?