B. 300Hz Step 1: Determine the wavelength ($\lambda$) from the diagram. The diagram shows 3 complete cycles of the wave over a distance of $3 \, \text{m}$. Therefore, the length of one wavelength is: $$\lambda = \frac{3 \, \text{m}}{3} = 1 \, \text{m}$$ Step 2: Identify the given wave speed ($v$). The wave travels with a speed of $300 \, \text{ms}^{-1}$. $$v = 300 \, \text{ms}^{-1}$$ Step 3: Calculate the frequency ($f$) using the wave equation. The relationship between wave speed, frequency, and wavelength is given by: $$v = f \lambda$$ To find the frequency, rearrange the formula: $$f = \frac{v}{\lambda}$$ Substitute the values: $$f = \frac{300 \, \text{ms}^{-1}}{1 \, \text{m}}$$ $$f = 300 \, \text{Hz}$$ The calculated frequency is $300 \, \text{Hz}$. This matches option B. The final answer is $\boxed{\text{B. 300Hz}}$.