Get selected values of MultiSelect Picklist in VisualForce

I have multiselect picklist and I want to get selected values for insert and update operation.

<apex:page standardController="Change_Request__c" sidebar="false" extensions="Change_RequestController"> 
  <apex:selectList label="Select Pasenger(s)" value="{!Change_Request__c.Passenger_Name__c}" multiselect="true" onfocus="getSelectedID('{!$Component.empid}');" >
      <apex:selectOptions value="{!pax}" />
  </apex:selectList>

And this is my extension:

public class Change_RequestController {
  private final Change_Request__c changer;
  public List<selectOption> pax;
  public Change_RequestController(ApexPages.StandardController controller) {
    this.changer = (Change_Request__c)controller.getRecord();
  }
  public List<selectOption> getPax() {
    List<selectOption> options = new List<selectOption>();
    String fullName;
    for (Passenger_Info__c p : [SELECT Id,First_Name__c,Name  from Passenger_Info__c ]) {
      fullName = (p.First_Name__c == null)?'':p.First_Name__c+' '+p.Name; 
      options.add(new selectOption(fullName, fullName));
     }
     return options;
  }
  public List<selectOption> setPax() {
    List<selectOption> options = new List<selectOption>();
    for (String pa : changer.Passenger_Name__c.split(',') ) {
      options.add(new selectOption(pa, pa));
     }
     return options;
  }
}