So velocity = 262 x 1.3 = 340.6 m/s
You've given us the wavelength and the frequency of the waves.
The only thing left for us to calculate is the speed of the waves.
Speed = (wavelength) x (frequency) = (1.3 m) x (256 / sec) = 332.8 m/s
This may or not be the accepted value for the speed of sound in air, but
it's consistent with the data you gave us.
