How to perform SUM operation in Entity Framework

I have a table.

create table tblCartItem(
pkCartItemId int primary key identity,
CartId int not null,
ProductId int not null,
Quantity int not null,
Price nvarchar(15)
)

and I want to perform sum opeartion on that like as

Select SUM(Price) from tblCartItem where CartId='107'

and I am trying to following code but its not working

ObjTempCart.CartTotal = (from c in db.tblCartItems where c.CartId == cartId select c.Price).Sum();

Any one help me to do this using Entity Framework. I am using MVC 4 Razor.