Solution
= Solution
Use an explicit Tully-Fisher-type scaling $L\propto v_{\max}^4$ for comparable spiral populations and photometric band. Relative to the preceding galaxy,
$$
\boxed{L_2\sim10^{10}(100/282)^4L_\odot\sim1.6\times10^8L_\odot.}
$$
The exponent and <normalization> are empirical and have scatter; one galaxy alone does not establish the relation. Different <Stellar population>[stellar populations], inclination errors and extinction change the photometric inference.