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.