529 and company tuition reimbursement

Hi - in 2021 tuition was 30k. 
1. employer assistance of 10k ($5250 tax free) received. 

2. 529 withdrawal amount to be determined 

 

Q. In order to avoid double dipping do I take 30k-10k? 

or 30k - 5250 tax free portion? 

Thank you in advance