"Data Validation" for Numbers

I'm not quite sure how to explain this, but this is my end goal.

In the attached file I want the sum of L4:T4 and L5:T5 to equal G7.

Columns L - T are assorted vendors, and each line item in my budget gets broken out among those vendors. I manual break up the subtotal as needed for that specific portion of a project, but sometimes either typos or addition / division errors result in the sum of the vendor cells not equaling the subtotal for that part of the project.

Is there a way to use something along the lines of data validation to have excel tell me if the sum of those cells doesn't match the subtotal in G7?

Thanks,
saq7792