【练习中】求大神指点

            List<Student> list = new List<Student>();

            list.Add(new Student { Age = 18, Name = "张三" });

            list.Add(new Student { Age = 17, Name = "李四" });

            list.Add(new Student { Age = 15, Name = "张三" });

            list.Add(new Student { Age = 19, Name = "李四" });

            list.Add(new Student { Age = 20, Name = "张三" });



            int sum = 0;

            foreach (var item in list)

            {

                if (item.Name.Equals("李四"))

                {

                    sum += item.Age;

                }

            }

            

            //现在想用list.ForEach(p => p.Name = "李四")  

            //这种拉姆达表达筛选出 名字为李四的年龄和