Function to read List Item Id based on task

taskListItemId = id of task item

web = Web object

SPListItem taskItem = taskList.GetItemById(taskListItemId);
Guid workflowInstanceId = new Guid((string)taskItem["WorkflowInstanceID"]);
SPWorkflow workflowInstance = new SPWorkflow(web, workflowInstanceId);
SPList itemList = workflowInstance.ParentList;
SPListItem parentListItemId = itemList.GetItemById(workflowInstance.ItemId);