If running fields aren't an option (why not, how does it not work?)...
Create a formula field for summing the values. In the formula, you can query other fields and sumarize only the values that meet some criteria.
I don't have CR installed at my new workplace, but the instructions are something along the lines:
For plain summary: right click the field, select formula / summary or something like that and select the operation SUM, field present_days
For formula, expand formula in the document layout on the left side (usually), right click and select new formula, give it a name and write your code.
Here is comprehensive tutorial with most common formula examples
If this helps please take time to accept the solution. Thank you.