Acertain wave has a wavelength of 45.0 meters and a frequency of 9.00 hz. what is the speed of the wave?

Hertz, which is a unit for frequency (f), also means 1/second. Hence, the speed (S) of wave is the product of its wavelength (n) generated per second (frequency). The speed of the given wave above is, 
 
                                     S = nf     ;   S = (45 m) x (9 / s) = 405 m/s

Hence, the speed of the wave is 405 m/s.