database

i need it to be solve in 30 minuts please

1. Based on the database schema above, answer the following questions: a. Find the primary key of each table. b. Find the forelgn key of each table. c. Define all possible Referential Integrity Constraints. d. Define two possible General Constraints. Based on the database schema above, generate the relational algebra expressions for the following: a. List all projects with maximum hours spent being more than 20. b. Find the phone number of the employees who worked on an assignment for more than 10 hours. 3. Based on the database schema above, write SQL expressions for the following: a. Select the project name and department only if the maximum hours spent are more than 20. b. Select the first name and last name of employees who have a phone number start with 281