Using the provided database answer the questions using relational algebra

• 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

A- Student(s) instructor with ID 15151 taught. We are interested in ID(s) and name(s) of this\those student(s).

B- Student(s) that got a grade A for both courses: CS-315 and CS-347.

C- Course section(s) taught by 2 instructors during the same semester and year.

D- Course ID(s) and name(s) that were never offered.