Enumerable.sum Method
        
 Computes the sum of the sequence of values that are obtained by invoking a transform
 function on each element of the input sequence.
 
         
         
        
            
 This method is static. 
        Parameters
        
            - source
            
 
            - 
                
Type: IEnumerable
A sequence of values to calculate the sum of. 
            - selector
            
 
            - 
                
Type: Function
A transform function to apply to each element.
Optional: True 
        
        Return Value
        
Type: Number
        
The sum of the projected values.