How to and how much discount you get when buying a crystal super

Use 12K Trade in value to buy Crystal Super

50% 12K trade in value (Up to $399 USD)
Eligible headsets can use part of their trade-in value for the Crystal Super. You can use up to 50% of your headset’s trade-in value for the Super, up to 399 USD, and keep the remaining trade-in value for the 12K.”

I don’t get it; how much of a discount do I get when buying an crystal super when owning an 8K and 8Kx. It is not clear to me.