Adding

Hi Ana-rosa, Thank you for the post and welcome to the forum, in answer to your question, you would set up a 3D formula, this is not as difficult as it sounds, follow these steps;
In the receiving worksheet in the cell you wish the result to appear, type = and your formula ie =SUM( then navigate to the sheet you wish to take information from and click on the cell you want, press the , (comma) and then navigate to the next location, click on the cell, continue in this vein if necessary, when you have exhausted the number of cells you wish to SUM close the brackets ()) and press ENTER.
I hope that has helped, best regards Pete