As we know by Doppler's effect
[tex]\frac{\Delta \lambda}{\lambda} = \frac{v}{c}[/tex]
so here we know that
[tex]\lambda' = 21.1 cm[/tex]
[tex]\lambda = 21 cm[/tex]
from above formula we have
[tex]\frac{21.1 - 21}{21} = \frac{v}{3 \times 10^8}[/tex]
[tex]\frac{0.1}{21} = \frac{v}{3 \times 10^8}[/tex]
[tex]v = 3 \times 10^8 \times \frac{0.1}{21}[/tex]
[tex]v = 1.43 \times 10^6 m/s[/tex]
so the galaxy is moving away from earth with above speed due to which we got larger wavelength
