$8\mathrm{.}23.$ Specify the following queries in relational algebra on the database schema in Exercise $5\mathrm{.}17$:a$.$ For the salesperson named 'Jane Doe', list the following information for all the cars she sold: Serial#$,$ Manufacturer, Sale$\_$price.b$.$ List the Serial# and Model of cars that have no options.c$.$ Consider the NATURAL JOIN operation between SALESPERSON and SALE. What is the meaning of a left outer join for these tables $($do not change the order of relations$)?$ Explain with an example.d$.$ Write a query in relational algebra involving selection and one set opera$-$ tion and say in words what the query does.