preventing ref errors

I am using the attached list and I want to calculate the total picked up revenue in B9 by utilizing the formula: =(B13*D13)+(B14*D14)+(B15*D15)

However, sometimes we will need to delete row 14 for example and then the above formula shows a ref error. How can I rewrite this formula to avoid the ref error from occuring.

I have made this much simplier and in truth I will have a very long list of room names in which I will be deleting rows at random.

Thank you!
Cate