PFAA student's estimated resources

Hello everyone, I am filling out the princeton financial aid application and is stuck at 1 question:
How much do your parents plan to contribute toward your 2016-17 college expenses?
My parents are seperated, never married. So should I enter the amount my Mother (custodial parent) can contribute Or the amount BOTH my parents can contribute? (note that there is another form for noncustodial parent)
Thank you.