theirs 
/ˈðeɚz/ pronoun
/ˈðeɚz/ pronoun 1 : that which belongs to or is connected with them : their one : their ones
▪ The computer is theirs. [=the computer belongs to them; it is their computer] ▪ He bought his car on the same day his parents bought theirs. ▪ She is a friend of theirs. [=she is their friend] ▪ That dog of theirs [=their dog] is always barking. 2 : his or hers — used to refer to a single person whose sex is not known or specified ▪ I will do my part if everybody else does theirs.
▪ The computer is theirs. [=the computer belongs to them; it is their computer] ▪ He bought his car on the same day his parents bought theirs. ▪ She is a friend of theirs. [=she is their friend] ▪ That dog of theirs [=their dog] is always barking.
