Given the following two tables, express in Relational Algebra the queries below: PC (model, speed, ram, hard_disk, price) Laptop (model, speed, ram, hard_disk, price) Express in Relational Algebra the following queries: a) List Laptop models with maximum ram 3 GB. [1 mark] b) List the details of pcs having price greater than 250 OMR and ram size greater or equal to 5 GO. [1 mark] c) List the capacities of hard disks that are available in PCs but are not available in laptops. [1 mark]

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Consider the following table: Instructor (Instructor_Id, Instructor_Name, specialization, Address, #Department_Id) Write in PL/SQL a function named NumberInstructor_department that takes the id of a department as an input parameter and returns the number of instructors who are working in that department.