$In$ the following equation hat$(y)=30,000+4xyin$ $$500xin$ dollars$$4in$ marketing $is$ associated with $a.an$ increase $of$ $$4in$ marketing $is$ associated with $an$ increase $of$ $$32,000in$ sales.

$b.An$ increase $of$ $$1in$ marketing $is$ associated with $an$ increase $of$ $$2,000in$ sales.

$c.An$ increase $of$ $$1in$ marketing $is$ associated with $an$ increase $of$ $$32,000in$ sales.

$d.An$ increase $of$ $$4in$ marketing $is$ associated with $an$ increase $of$ $$2,000in$ sales.