We will determine the wavelength through the relationship given by the distance between slits, this relationship is given under the function
[tex]y = \frac{m\lambda}{d}[/tex]
Here,
m = Number of order bright fringe
[tex]\lambda[/tex] = Wavelength
d = Distance between slits
Both distance are the same, then
[tex]y_1 = y_2[/tex]
[tex]\frac{m_1\lambda_1 r}{d} = \frac{m_2\lambda_2 r}{d}[/tex]
[tex]\frac{m_1\lambda_1}{m_2\lambda_2} =1[/tex]
Rearranging to find the second wavelength
[tex]m_1 \lambda_1 = m_2 \lambda _2[/tex]
[tex]\lambda_2 = \frac{m_1\lambda_1}{m_2}[/tex]
[tex]\lambda_2 = \frac{7(629)}{8}[/tex]
[tex]\lambda_2 = 550.3nm[/tex]
Therefore the wavelength of the light coming from the second monochromatic light source is 550.3nm