VS 2010 Speeding Up My Code

Code:

  Dim str As String = "something bla bla "

If CheckBox3.Checked Then  

                          For Each itm As String In ListBox2.Items

                                If str.Contains(itm) Then

                                    Dim imp As String = "Something here"

                                    For Each pair In list

                                        If pair.Contains(imp) Then

                                            id = pair.Replace(imp, "")

                                        End If

                                                                            Next

                                     End If

                            Next

                        End If

Is there any shorter and faster way to do this ?
also im reading the strings into a list of strings which are in this format :

Quote:

Example 45432

Quote:

Example1 85859

Again, is there any alternative way to do this in a faster way i should be able remove the whole string in list if half of the string matches ?