Two waves of equal frequency f and velocity v travel in opposite directions along the same path. The waves have amplitudes A and 3A. Then

y=y1+y2=A sin (ωt−kx)+3A sin (ωt+kx)=A sin ωt cos kx−A cos ωt sin kx+3A sin ωt cos kx+3A cos ωt sin kx=4A sin ωt cos kx+2A cos ωt sin kx=2A sin ωt cos kx+2A sin (ωt+kx)It is combination of a stationary and travelling wave.Maximum amplitude = 4 A.Minimum amplitude = 2 ADistance between points having amplitude 4A and 2A will be =λ/4=v/4f