According to the task there should be the graph that supports Sally's hike, but after looking on the options it seems that Sally doesn't walks at a constant rate and there is the negative option that coincides with my thoughts. So, I bet the false statement is the third option represented in the scale above.
Answer:
Wave speed = Wavelength x Frequency
26 m/s = Wavelength x 49
Divide by 49 to find the wavelength:
The wavelength is approximately 0.53
Let me know if this helps!