Formula to help decide percentage distribution based on ultimate budget

Hi,

I work in media planning and came across a challenge which seems like it could be solved by a very logical formula or function. I just dont know how to do it.

In the attached document you can see my budget in yellow in the far right. The percentages in orange are the ones that need to change (either go up or down but obviously still equal 100%) to meet the budget and not exceed it.

I have been doing this manually and playing around with different variations to meet the budget. However, I have multiple markets to do so that's when I began exploring online for a solution in the form of a function or formula.

Any help would be greatly appreciated!!!

I added some comments to clarify.

Let me know if this helps.

Appreciate any help!