**I have a table with 4 columns = a(ID),b,c and d.By using LINQ, how can I calculate 'd'* 'b' / 'c' while changing 'a' with a combobox?And would it make any difference if it is a VIEW? is it a fair question? and do you need more information? **

Don't know how your list looks, but it should be something like this:

var a = 1; // your dropdown value
var result = list.Where(item => item.A == a).Select(item => item.D * item.B / item.C);