How to distribute values using priority

Hello,

I am really struggling with a complex formula, not sure how best to achieve it.

I have a set of quantities that need to distributed according to a priority, and maximum rule.
I have attached a sample file to explain a little better, if anyone could help or point me in the right direction that would be great.
Thanks.

Thanks Kaper, sorry for the delay... the original sample I attached was too simple compared to my requirement sorry. I have created another along the same lines, the tricky bit for me is using the priority to distribute the quantities.
I have attached actually my real world sample, if you can work your magic and give us a formula it would be fantastic, I have been pulling my hair out for days to try and find a formula to automate it.