I am preparing a regression analysis of sales data and advertisement data. The sales data is from Monday to Sunday, but Sundays have a value of 0 because the store is closed. The advertisement data from Monday to Sunday has values way greater than 0 on Sunday. It is for a Marketing Mix Modeling project.

How can I deal with that? Is that called noisy data or something else? Do I just remove the Sunday altogether?

Thank you in advance for any hints how to research that further.