The increase demanded of Fairfax County is 6.7%, not 4.8%.
To balance the budget, a 6.7 percent increase in funding from the County is needed.
And that assumes that the state will continue to fund 15% of the total FCPS budget, despite the massive spending increase proposed.
http://www.fcps.edu/news/fy2017/docs/fy17budgetoverview.pdf