For each query, complete the relational algebra query.

• classroom
• building string
• room_number number
• capacity number
• department
• dept_name string
• building string
• budget number
• course
• course_id string
• title string
• dept_name string
• credits number
• instructor
• ID number
• name string
• dept_name string
• salary number
• section
• course_id string
• sec_id number
• semester string
• year number
• building string
• room_number number
• time_slot_id string
• teaches
• ID number
• course_id string
• sec_id number
• semester string
• year number
• student
• ID number
• name string
• dept_name string
• tot_cred number
• takes
• ID number
• course_id string
• sec_id number
• semester string
• year number
• grade string
• advisor
• s_id number
• i_id number
• time_slot
• time_slot_id string
• day string
• start_hr number
• start_min number
• end_hr number
• end_min number
• prereq
• course_id string
• prereq_id string