What we want to mean when talking about voice is how the subject and the verb are related in a sentence. In this way, the passive voice is used when the subject receives the action. So, in this exercise the formula we must use is:
se + third person of the verb
The verb in this sentence is bailar (to dance), so the conjugation of this verb for the third-person singular is baila, therefore the right answer is:
Se baila salsa
whose meaning in English is:
Salsa is danced
Salsa is a type of music that is danced in countries like Puerto Rico, Cuba, Dominic Republic, Venezuela and Colombia.
