write a select statement that answers this question: what is the total number of courses taught by parttime instructors? return these columns: the instructor last name and first name from the instructors table in this format: doe, john (note: if the instructor first name has a null value, the concatenation of the first and last name will result in a null value.) the total number of courses taught for each instructor in the courses table use the rollup operator to include a row that gives the grand total.