Given an online DVD rental system $($e$.$g$.$ blockbuster$),$ the system provide both rental and buying services.

Entertainment items include DVDs of movie, game, TV series, learning materials. The company provides different

packages for DVD rental: $$9\mathrm{.}99$ for $10$ DVDs for one month, $$19\mathrm{.}99$ for $30$ DVDs for one month, and $$29\mathrm{.}99$ for

$50$DVDs per month. The website provides interface for the payment. Mailing and returning of DVDs should be

properly taken care of by the web.

a$)$ Define all necessary classes for the system. $(4)$

b$)$ Prepare a class diagram for the system. $(3)$

c$)$ Prepare a state$-$chart diagram for the system. $(3)$