"Is it eight or eighty?"
Translation:An ea ocht nó ochtó?
I am playing devil's advocate - the sentence is a classification sentence, and also it's a question sentence. The classification part requires the copula. If you look at the first definition of "ea" in: https://www.teanglann.ie/en/fgb/ea , you will see ea is used in classification copula to mean the 3rd singular neuter pronoun. Also, "ea" is located right after the copula initiator word, which in this case is "an". I hope I've helped.
It's true those are classification sentences, but they're a special form of the classification sentence. In that example ea is a stand-in referring back to múinteoir which appears in front of the copula for emphasis. Here nothing is appearing in front of the copula so there's no reason for the ea substitution. Theoretically this special form can be turned into a question, An múinteoir is ea an bhean but I can't say I've actually encountered it. In either form an ea doesn't appear in a classification-type question.
As for the suitability of the classification copula at all I think any scenario where I'd have to classify things as "an eight or an eighty" would be vanishingly rare compared to more mundane questions like "Is it eight or eighty centimeters?" or "Are there eight or eighty people there?" Neither of these two questions demand the copula, and on account of their higher occurrence I'd prefer Duolingo work from their template, rather than attempt and botch a copular construction.