Getting index of all items containing a value using Linq

Question

I am just starting to learn Linq.

and i have this list 

string[] names = { "jack", "harry", "James", "peter" };
            List <string> list32 = new List<string>(names);

 I would like to get all the index numbers of the items that contain a specific char

i have tried this

var mylinqQuery = from f in list32
            where f.Contains('a')
            select f;

 but it only returns the full names

 Can somebody help me with this