Consider the following queries for the Northwind database. Write in relational algebra queries $($a$)($e$)$ and in SQL all the queries.

a$.$ Name, address, city, and region of employees.

b$.$ Name of employees and name of customers located in Brussels related through orders that are sent by Speedy Express.

c$.$ Title and name of employees who have sold at least one of the products "Gravad Lax" or "Mishi Kobe Niku.$*$

d$.$ Name and title of employees as well as the name and title of the employee to whom they

e$.$ Name of products that were sold by employees or purchased by customers located in London.

f$.$ Name of employees and name of the city where they live for employees who have sold to customers located in the same city.

g$.$ Names of products that have not been ordered.

In$.$

Names of customers who bought all products.

Name of categories and the average price of products in each category.

Identifier and name of the companies that provide more than three products.

k$.$ Identifier, name, and total sales of employees ordered by employee identifier.

$1.$ Name of employees who sell the products of more than seven suppliers.