Why is the Wave length 0.40m

The wavelength was given as $40 \text{ cm}$. To convert centimeters to meters, you divide by 100, because there are $100 \text{ cm}$ in $1 \text{ m}$.

$$40 \text{ cm} = \frac{40}{100} \text{ m} = \boxed{\text{0.40 m}}$$