Easy is the opposite of Dense. Dense is a synonym of Tough. Tough is related to Steak. 
Rubber is derived from Rub. File entails/necessarily involves Rub. you are likely to find File in/at/on Computer. 
Easy <--Antonym--> Dense <--Synonym--> Tough <--RelatedTo--> Steak 
Rubber --DerivedFrom--> Rub <--Entails-- File --AtLocation--> Computer 