Suppose that only 80% of the student records from exercise 16.28 have a value for phone, 85% for major_dept_code, 15% for minor_dept_code, and 90% for degree_program; and suppose that we use a variable-length record file. each record has a 1-byte field type for each field in the record, plus the 1-byte deletion marker and a 1-byte end-of-record marker. suppose that we use a spanned record organization, where each block has a 5-byte pointer to the next block (this space is not used for record storage). a. calculate the average record length r in bytes. b. calculate the number of blocks needed for the file.