How do I solve the problem?
It looks like you may have not included the correct namespace for CombatTarget, I also noticed possibly the namespace may be incorrect your fighter namespace.
Paste in the text of CombatTarget.cs, as well as the text to the two scripts you’ve posted as text instead of as a screenshot, and we’ll take a closer look.
After pasting in each script, select what you’ve pasted and click the </> button to format the text so it is easily readable as code.