The formula for the speed of a wave is:
`s = lambda/T`
where `s` is the speed of the wave
`lambda` is the wavelength
`T ` is the period
Then, substitute the given values to the formula.
`s = lambda/T = 31/0.18 = 172.22` cm/s
Among the choices the nearest value is 170 cm/s.
Hence, the speed of the wave is (c.)170 cm/s.