Conditional Formatting - with two conditions within one formula

Hi everybody, this is my first post

I am trying to use conditional formatting for a cell;

It is a cell using Validation; you can choose "Yes" or "No" from a list
If the value is "Yes" the cell should be green, regardless of everything else
But if the value is "No" it should turn red, but only if a choice in another cell is equal to "X". Otherwise it should be left without special formatting.

Anybody have any idea on how to do this?

I have attached a file which is trying to explain this in more detail.

Grateful for any advice, thanks. / D

See the attached file.