It's still confusing because I how did you get 3 I mean the three you divided with

• A complete wavelength ($\lambda$) consists of one full cycle (e.g., one crest and one trough).
• Looking at the diagram:
  • From $0 \, \text{m}$ to $1 \, \text{m}$, there is $\text{1 complete wavelength}$.
  • From $1 \, \text{m}$ to $2 \, \text{m}$, there is a $\text{2nd complete wavelength}$.
  • From $2 \, \text{m}$ to $3 \, \text{m}$, there is a $\text{3rd complete wavelength}$.
• So, there are $\text{3 complete wavelengths}$ shown within the total distance of $3 \, \text{m}$.

Since 3 complete wavelengths fit into $3 \, \text{m}$, the length of one wavelength ($\lambda$) is: