What is the answer? <--What's the subject?
Solution 1:
In this question, the answer is the subject.
Questions often reverse the typical syntactic order of noun then verb. Subject-auxillary inversion is frequently employed in English to form questions.
The question at hand can be dissected and reassembled as:
The answer is what?
Had it been phrased in this more awkward but grammatically correct manner, the subject is much more readily apparent.