Correct answer: 9/4
The longest wavelength in a series corresponds to the transition to the lowest energy level of that series. For the Lyman series, this is n=2 to n=1, and for the Balmer series, it is n=3 to n=2. Using the Rydberg formula, the ratio of wavelengths is (n₁²/n₂²) = (2²/3²) = 4/9.