c# - Sum of Columns of Two Tables in LINQ -

i have 2 related tables in ms sql.

example... table – room roomid roomcost  table b – roomitem roomitemid itemname itemcost roomid 

i need in writing linq code add roomcost sum itemcost (if have same roomid) , post results in wpf textbox. far have tried

dataclassesdatacontext dc= new dataclassesdatacontext(); var roomamount = (from dbo in dc.room select dbo.roomcost).single(); var itemamount = (from itm in dc.roomitem select itm.itemcost).single(); decimal rmamount = convert.todecimal(roomamount); decimal itmamount = convert.todecimal(itemamount); decimal tamount=rmamount+itmamout; txttotalamount.text=tamount 

i beginner in c#, kindly help. if haven't been clear enough, ask.

how using sum() (havent tested it):

assuming room.roomcost decimal , roomitem.itemcost decimal , myroomid id of room want sum up:

var roomamount = dc.room.single(r => r.roomid == myroomid).roomcost; var itemamount = dc.roomitem.where(i => i.roomid == myroomid).sum(r => r.itemcost);  txttotalamount.text= roomamount + itemamount ;