It is very easy really, you just need to take the EL (eperience level) of the strongest leveled Digimon in the DNA digivolution, then take the weakest Digimon's El and divide it by 5. Then add that number to the strongest Digimon's level and that will be the level of your new DNA digivoled Digimon!

Example: 35+(22 divided by 5)
=35+(4)
=39

Note: When dividing the two numbers remember to NEVER round up. Always round down even if it comes out to .9.