Astring, 68 cm long and fixed at both ends, vibrates with a standing wave that has 3 antinodes. the frequency is 180 hz. what is the wave speed?

The given situation below describes a standing wave because the string is fixed at both ends. A standing wave having three anti-nodes will have a wavelength that is two-thirds the length of the string. After getting the wavelength, this can be multiplied with the frequency to get the wave speed. 

For this problem: 

wave length = (2/3)(length of string: 68 cm)
wave length = (10/3 cm)

wave speed = wave length x frequency
wave speed = (10/3 cm) x (180 Hz)
wave speed = 600 cm/s or 0.6 m/s

Sorry i don’t know what to do