Consider the relational schema below: Students(sid: integer, sname: string, major: string) Courses(cid: integer, cname: string) Enrollment(sid: integer, cid: integer, grade: real) Write a tuple relational calculus expression that satisfies this query? Find the distinct names of all students who major in either "Math" or "Economics" who score less than 60% in either course 91.573 or in course 14.601 (using cid).