1. If "sabes" refers to the formal "usted" (you formal):
* Sabía la respuesta - This translates to "You knew the answer."
2. If "sabes" refers to the informal "tú" (you informal):
* Sabías la respuesta - This translates to "You knew the answer."
3. If "sabes" is part of a compound tense like the imperfect subjunctive:
* Supiera la respuesta - This translates to "If you knew the answer."
4. If "sabes" is part of a compound tense like the conditional simple:
* Sabría la respuesta - This translates to "You would know the answer."
Therefore, the exact past tense of "sabes la respuesta" depends on the intended subject and the grammatical context.