Quest of Nine

The Book

What function?

Can you work out what function has been carried out on the numbers on the left to change them to the numbers on the right?

inputfunctionoutput
3arrow?arrow15
12arrow?arrow24
7arrow?arrow77
14arrow?arrow-1
120arrow?arrow60
49arrow?arrow7
23arrow?arrow-5
0arrow?arrow17

Is there only one right answer? - or can you think of more than one function to give the same output?