A 1 metre long tube open at one end, with a movable piston at other end

A 1 metre long tube open at one end, with a movable piston at other end, shows resonance with a fixed frequency source (a tuning fork of frequency 340 Hz) when the tube length is 25.5 cm or 79.3 cm. Estimate the speed of sound in air at the temperature of the experiment The edge effects may be neglected.