Hello everyone
I am having trouble solving this problem an I really need some help:

a mechanical engineer who recently graduated is contemplating starting his own business. He can purchase a web page design aimed at delivering information only for $600 a year. If the business is sucessful, he will purchase a more elaborate e- commerce pakage costing 4000 $ a year. if he purchases the 600 $ package now for two years, after which he will abandon and purchase the 4000 $ package, what is the equivalent annual worth for a period of 6 years? Use a 12 % interest rate

Ok I know that the EAW=PW*(A/P,12%,6)
but i am having difficulties finding the PW where PW=PWB-PWC

Thank you for helping