Health related is the correct way to write this. So your answer is two words.
An example sentence is: They will assess whether his problem is mental health related.
It's spelled with one word.
one word
Two, "as well."
Overcomes is one word.
the word centerpiece is one word
No, you have spelled letterhead correctly as one word.
Could be spelled firsthand, one word, or first-hand.
1 word
The word reunion is spelled as one word, not hyphenated.
embarrassed (the same way you spelled it!)
one word, but 2 syllables. Spelled: payback. :)
"Carryover" is typically spelled as one word.