Sum of totals in object

Not sure if this is the correct forum but using c#, so anyway...
Basically I have an object that has totals (example below) and what I am trying to do is sum those totals per section ID and wondering what is the best way? I could loop through the object a second time and sum them up that way I guess, but wondering if there is a better/quicker way with LINQ or maybe in SQL itself to get a count of counts???
ID    Total  SectionID
1        20      6
2        15      6
3        4        3
4        7        3
 
 
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