Question

A wave of infrared light has a speed of 6 m/s and a wavelength of 12 m. What is the frequency of this wave?

Answer 1

Frequency(ν) = speed of infrared light( c )/wavelength( λ ) = 6/12 = 1/2 = 0.5 s^-1 . 

Answer 2

I'll be happy to solve the problem using the information that
you gave in the question, but I have to tell you that this wave
is not infrared light.

If it was a wave of infrared, then its speed would be close
to 300,000,000 m/s, not 6 m/s, and its wavelength would be
less than 0.001 meter, not 12 meters.

For the wave you described . . .

             Frequency  =  (speed)  /  (wavelength)

                                 =  (6 m/s)  /  (12 m)

                                 =      0.5 / sec

                                 =      0.5 Hz .  

(If it were an infrared wave, then its frequency would be
greater than 300,000,000,000 Hz.)