Why can't the answer for 26 be trial 3 as well.. The answer is trial one. But If you take the initial height minus the given water height of trial 3 you get 12.5 . And if you multiply this by two you get 25 .
In the f = nv/4L equation, you have to remember that n can only be an odd integer (since this is a closed-open system). So if the fundamental mode (n=1) is 340, the next harmonic would be 1020 (for n = 3).
