Juan, sorry this got missed. If you're still looking for an answer then see attached.
Basically you're running into a limit of Data Blending. You can more easily get your result using Tableau's Multiple Tables data connection option:
But before you set that up, you'll want to put the worksheets in the same Excel workbook. When you do a join like this you're data can get doubled, which is why I created those field calculations to divide those measures by two before summing them on the row shelf.
Hope this helps,
Thanks a lot Shawn!!! That was exactly was I was trying to get. I also got it by changing the data: I deleted the field "Type" for the capacities, and split the field "Capacity" in two different fields, one @for each type of capacity. In that way I was able to drag and drop each measure into the same chart with the same structure of data blending.
Anyway this much easier as you said.