How to save work book while automation Excel

Question

this may be a silly question with a simple answer but I am automating ecxel from a windows form and in a click event I have:

Excel.Application objExcel = new Excel.Application();
Excel.Workbook objWorkBook = objExcel.Workbooks.Add(System.Reflection.Missing.Value);
Excel.Worksheet objSheet = (Excel.Worksheet)objWorkBook.Worksheets.get_Item(1);

//do stuff to sheet in workbook


but how do I save the work book to a specific location?