Work out the villain first: head, body and legs together make his strength.
Your hero has to be exactly that strong. Start with the head and see how much is still missing.
You have to make that rest from body and legs - only a few options there.
If it does not work out, take the next head part. That way you try everything in order instead of guessing.
Example
For parents
What does this exercise practice?
Building heroes joins two steps - first add three numbers, then rebuild that same total from exactly three parts.
Common pitfalls
The hero has to match the villain exactly, not beat him. And it has to be exactly three parts - one from each column.
How to practice at home
Make three piles of numbered slips, draw one from each and add them up - the next player has to match that total with their own slips.