\(y=A_0 \sin (k x) \cos \omega t\)
Mid way between a node and antinode is \(\frac{\lambda}{8}\) from origin. Function for amplitude is \(A=A_0 \sin (k x\)
\(A=4 \sin \left(\frac{2 \pi}{\lambda} \times \frac{\lambda}{8}\right)\)
\(A=2 \sqrt{2} \,cm\)