How fast a person should drive his car so that the red signal of light appears green? (Wavelength for red colour$=6200 \mathrm{\AA }$ and wavelength for green colour$=5400 \mathrm{\AA }$.)

With what speed should a galaxy move with respect to us so that a certain line at $674 \mathrm{nm}$ is observed at$674.4 \mathrm{nm}$?

The spectral line emitted by a star, has a wavelength of $6800 \mathrm{\AA }$ when observed from a lab appears to have a wavelength $6820 \mathrm{\AA }.$ Speed of star in the line of light relative to earth for receding or approach is given by

The positive shift occurred in the wavelength of the light received from the star is $0.025\%$. What is the velocity of star in the line of light ?