My child is attending her first year at college and I am seeking to have my child support reduced as I am now responsible for 50% of her room and board. I/we have been awarded financial aid which has offset the cost of the yearly tuition room and board. How am I to figure what percentage of the child support I can take back to apply to college room and board. Is it computed prior to the financial aid or after. I need to suuply this figure in court as my ex spouse is claiming the majority should still go to child support. Is there a formula I can follow or previous case law that I can refer to.

Thanks for your help.