"I am well."
Translation:Me bene habeo.
It's a reflexive construction.
"Bene ego" doesn't have a verb. While colloquial, classical Latin sometimes omits "to be," the sentence "bene ago" ("I am faring well") is more grammatical.
A few reasons:
"est" is the 3rd person conjugation. You need to say "ego sum". It's "I am" after all, not "I is".
"bene" is strictly an adverb. It does not compare with the English "well" which is an adjective when used to discuss health.
"Me bene habeo" is idiomatic in Latin. It's literally "I hold myself well", thus "bene" is an adverb modifying "hold," which is an active verb.
Stative verbs such as "esse/to be" take adjectives because as verbs of state, anything in the predicate is a subject complement, meaning it directly modifies the subject, not the verb.
I think "valeo" is an acceptable answer, but I jumped right to the placement test so the test may only want the answers that were used in "learn" mode.