Physics double source interference? 10 points?

Two point sources, 5cm apart are operating in phase, wih a common frequency of 6Hz, in a ripple tank. A metre sick is placed above the water, parallel to the line joining the sources. The first nodal lines (the ones adjacent to the central axis) cross the metre stick at the 35cmm and 55cm marks. Each of the crossing points is 50cm from the midpoint of the line joining the two sources. calculate the wavelength and speed of the waves.