Adding to Maulik V's answer, there's a slight difference between the pronunciation of 

>**box** **/ˈbäks/** 

and 

>**bucks** **/ˈbəks/** 

I know it's not easy to differentiate for some (and up to some point), but if you'd try to listen carefully, you'd be able to distinguish properly (also, context clues).

(pronunciations were taken from http://www.merriam-webster.com/)