"I think that he will be fine."
Translation:Mi pensas, ke li fartos bone.
"Be" does not mean "feel." In English, "I am fine" may not mean "I feel fine." In context it might mean that, but out of context it cannot, and no sentence in duolingo has any context.
Esti does mean "to be", and we use it that way in English, but not in Esperanto. Farti is how someone is doing, how they fare, not how they are being.
Li fartas bone - he is doing well, or he is faring well. Li estas bone - He is being well, he is doing a good job of being.
I consider that will be fine should be translated as: ....estos bonega. As you modify esti, bone becomes bona. Is this correct?
No, it's not. Bonega means "very (or bigly) good" and we are not being asked for degrees of fineness, so bonege would also be in error. What we are supposed to be modifying here is farti not esti (even though esti is apparently now accepted) and farti is all about how one is feeling.
Mi esperas, ke tiu helpas.
maybe the English version should be "will feel fine"; I was just fooled by this drill because it lacked context, and 'estos' was NOT accepted, even though some posts suggest it was at some point.
Aŭ kredas, ĉu?
Oni povas ankaŭ uzi "Laŭ mi". Sed neniu de tiuj estas la leciono