SQL Server 2019

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DECLARE @x table(number int,     grade char(1),    weight int);

INSERT @x(number,grade,weight) VALUES
(1         ,'A',         185),
(2         ,'A',         179),
(3         ,'C',         191),
(4         ,'C',         192),
(5         ,'C',         193),
(6         ,'A',         194),
(7         ,'A',         196),
(8         ,'A',         188),
(9         ,'A',         187),
(10        ,'A',         200),
(11        ,'B',         201),
(12        ,'B',         202),
(13        ,'B',         203),
(14        ,'B',         191),
(15        ,'B',         187);

-- 2017+
    ;WITH x AS 
    (
      SELECT g = grade, 
             y = CONCAT('Count$g',COUNT(*),' , Sum$g',SUM(weight)) 
      FROM @x
      GROUP BY grade
    )
    SELECT STRING_AGG(REPLACE(y, '$g', ' of ' + g + ' : '), ' - ')
           WITHIN GROUP (ORDER BY g)
    FROM x;
    
--2012-2016
    ;WITH x AS
    (
      SELECT g = grade, 
             y = CONCAT('Count$g',COUNT(*),' , Sum$g',SUM(weight)) 
      FROM @x
      GROUP BY grade
    )
    SELECT STUFF((
        SELECT ' - ' + REPLACE(y, '$g', ' of ' + g + ' : ') 
          FROM x 
          ORDER BY g 
          FOR XML PATH, TYPE).value(N'.[1]','nvarchar(max)'), 1, 3, '');
          
-- 2005, 2008, 2008 R2

;WITH x AS
    (
      SELECT g = grade, y = 'Count$g'  + CONVERT(varchar(11), COUNT(*))
                          + ' , Sum$g' + CONVERT(varchar(11), SUM(weight)) 
      FROM @x
      GROUP BY grade
    )
    SELECT STUFF((
        SELECT ' - ' + REPLACE(y, '$g', ' of ' + g + ' : ') 
          FROM x 
          ORDER BY g 
          FOR XML PATH(''),type).value(N'.[1]', N'varchar(max)'), 1, 3, '');

(No column name)
Count of A : 7 , Sum of A : 1329 - Count of B : 5 , Sum of B : 984 - Count of C : 3 , Sum of C : 576

(No column name)
Count of A : 7 , Sum of A : 1329 - Count of B : 5 , Sum of B : 984 - Count of C : 3 , Sum of C : 576

(No column name)
Count of A : 7 , Sum of A : 1329 - Count of B : 5 , Sum of B : 984 - Count of C : 3 , Sum of C : 576