Answer
Temperature of red star T= 4142.857 K
(we can approximate it by T= 4143 K)
Work Step by Step
Wavelength of maximum emission for red star is $\lambda_{max}=700 nm=700\times10^{-9}m =7\times10^{-7}m$
From Wiens displacement Law $\lambda_{max} T = 2.90\times10^{-3}$ m.K
so $ T= \frac{2.90\times10^{-3} m.K}{\lambda_{max}}$
putting the value of $\lambda_{max}=700\times10^{-9}$ m in above equation we will get
$ T= \frac{2.90\times10^{-3} m.K}{7\times10^{-7} m}$
so T= 0.4142857$\times 10^{4}$ K
T= 4142.857 K
