In a query you can just do something like:

SELECT ColumnA * ColumnB FROM table

or

SELECT ColumnA - ColumnB FROM table

You can also create computed columns in your table where you can permanently use your formula.

select InitialPayment * MonthlyPayRate as SomeRandomCalculation from Payment

Syntax:

SELECT <Expression>[Arithmetic_Operator]<expression>...
 FROM [Table_Name] 
 WHERE [expression];

1. Expression : Expression made up of a single constant, variable, scalar function, or column name and can also be the pieces of a SQL query that compare values against other values or perform arithmetic calculations.
2. Arithmetic_Operator : Plus(+), minus(-), multiply(*), and divide(/).
3. Table_Name : Name of the table.

This code is used to multiply the values of one column

select exp(sum(log(column))) from table

You can use the query:

for multiplication

Select columnA * cloumnB as MultiplyResult from TableName

for subtraction

Select columnA - cloumnB as SubtractionResult from TableName

select InitialPayment * MonthlyRate as MultiplyingCalculation,
InitialPayment - MonthlyRate as SubtractingCalculation
 from Payment