如何在一个LINQ上获得children值的总和

这是我的结构：

程序-描述等…

操作-程序Id、说明等。

成本-Action_Id、Value1、Value2、Value3

一个操作可以有多个成本。我需要的是一个按程序对这些值进行分组的查询。类似：

"程序名称"|总值1 |总值2 |程序总额

这是我迄今为止的努力：

var ListByPrograma = from a in db.Actions
    join c in db.Costs on a.Id equals c.Action_Id
    group a by a.Program into p
    select new 
    {
        Program = p.Key,
        actionsQuantity = p.Count(),
        totalValue1 = p.Costs.????
        totalValue2 = ?,
        totalByProgram = ?
    };

var ListByPrograma  = from a in db.Actions
 join c in db.Costs on a.ID equals c.Action_Id
 group new {a,c} by a.Program into p
 select new
 {
    Program = p.Key,
    actionsQty = p.Count ( ),
    totalValue1 = p.Sum(y => y.c.Value1),
    totalValue2 = p.Sum (y => y.c.Value2),
    totalValue3 = p.Sum(y=>y.c.Value3)
};