Middle C on a piano vibrates at 262 Hz. The sound waves produced by this string have a wavelength in air of 1.30 m. What is the speed of the sound waves?

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.