Hi. 'Run the numbers' generally means 'do the calculations' (especially financial calculations). In business situations when people are deciding whether they can afford to embark on a project, make a purchase, make an investment, etc., the people who make the decisions say, 'run the numbers by me and let's see if it makes sense', meaning 'show me the financial calculations/the data/the maths and then we can make a decision'.

This expression means that someone will do some numerical calculations for another person. This phrase is often used in the financial and accounting areas of business, especially when one is dealing with budgets and/or important figures for a potential client of some business. Often the person "running the numbers" may be called a "numbers man" if that person is good at doing the calculations, is very good with business math in general, and is the one people usually go to for "running the numbers". As for why do we do these calculations, the numbers may be run so that a decision can be made by someone. But, numbers are also run to verify figures for other reasons, such as in accounting before submitting finalized reports where the numbers are critical and need to be accurate.