Hello, thank you for taking the time to post your question!
In that formulation y = 35000 + 0.45x, the base salary is $35,000 because that is what he earns if x = 0. The percent commission then is the 0.45 or 45%, meaning that per sale he earns 45% of the sales.
Most likely then we will not be able to use the same equation for Tom next year because typically a contract like this would be negotiated on a yearly basis. So the base salary, the commission percentage, or both might change in the new year
I hope that helps you get moving in a better direction on this type of question! Feel free to reach out if you have any additional questions beyond that :)