\(B=2 \times 10^{-7} \sin \left(0.5 \times 10^{-3} x+1.5 \times 10^{11} t\right)\)

\(f=\frac{c}{\lambda}, \quad k=0.5 \times 10^{-3}\)

\(\omega=1.5 \times 10^{11}\)

\(V=\frac{\omega}{k}=\frac{1.5 \times 10^{11}}{0.5 \times 10^{-3}}=3 \times 10^{14}\)

\(\frac{\omega}{k}=f \lambda\)

\(k=\frac{2 \pi}{\lambda}\)

\(\therefore \lambda= \frac{2 \pi}{k}=\frac{2 \times 22}{7 \times 0.5 \times 10^{-3}}={1.25 \times 10^4} \,m\)