problems with the interdependency between surfaces

Hi together. I´m a beginner with the grasshopper programm and I hope somebodey can help me.

OK. I have a main surface, which I want to split in 3 parts. I want on at the first part to add an slider, which I can say how may % this part has to be from the main surface. With the second part, I want to make nearlly the same like with the first part, but now I want that the second part stands in dependency with the leftover of the main surfaces (main surface - first part = leftover). I also want to add an slider on the second part.

In the end, I want to see how much remain of the main surface, if I say ,for example, the first part is 40% from the main surface and the second part is 60% from the leftover.

I really hope, that there is somebody who can help me with this kind of problem!!!