= Solution
At this small <redshift>, $D\simeq cz/H_0\simeq20.0$ Mpc. The outer angular <radius> gives $R_{\rm out}\simeq D\theta\simeq21.3$ kpc. Approximating the dynamical <mass> by a spherical equivalent,
$$
\boxed{M_{\rm dyn}(<R_{\rm out})\simeq\frac{V_{\rm rot}^2R_{\rm out}}G
\simeq4.9\times10^{11}M_\odot.}
$$
The supplied <Tully-Fisher relation> gives $M_V\simeq-22.49$, and hence $L_V\simeq9.9\times10^{10}L_{V,\odot}$. Treating the population as solar-like gives the estimate $\Upsilon_V\simeq1\,M_\odot/L_{V,\odot}$, so
$$
\boxed{M_{\rm luminous}\simeq1.0\times10^{11}M_\odot.}
$$
The dynamical estimate exceeds that by about a factor of five; a massive extended dark-matter component is the natural interpretation. Solar-like spectra do not exactly fix the population <mass-to-light ratio>, and a disk is not spherical, but order-unity corrections do not remove this large outer <mass> excess under the stated estimate.
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