Answer :
Wavelength of the wave = 30 cm
Converting it into meters:
Wavelength = [tex]\frac{30}{100} = 0.3[/tex] m
Frequency of the wave = 15 Hz
Let the speed of the wave be v.
The relation between wavelength, frequency and speed of the wave:
Speed = frequency x wavelength
Speed = 15 x 0.3
Speed = 4.5 m/s
Hence, the speed of the wave = 4.5 m/s
Hence, option A is correct.