Correct answer: 330 m/s
The beat frequency is given by the difference in frequencies of the two waves: n = |f1 - f2|. Using the relation v = fλ, we find f1 = v/λ1 and f2 = v/λ2. Substituting these into the beat frequency equation, we get n = v(1/λ1 - 1/λ2). Solving for v using n = 12, λ1 = 0.5 m, and λ2 = 0.51 m, we find v = 330 m/s.