I hope you all had an amazing holiday weekend. Currently, I have a dataset that includes company name, company type, service provided, charge for the service, and this is all by month. For example, Company X, type of company is a bank, services provided are debt portfolio evaluations at $100 and data analytics at $3,500, and the month is November (obviously this is a fictional example). There would be two entries for this company because there are two services. What regression model would you recommend to calculate if a company is being under billed?