Distance and Evolutionary States of Supernova Remnant G18.9-1.1 and
  Candidate G28.6+0.0
  HI spectra of the supernova remnant G18.9-1.1 and the supernova remnant
candidate G28.6+0.0 are analyzed. We compared the spectra to $^{13}$CO emission
spectra and to spectra of HII regions in the area to determine kinematic
distances. G18.9-1.1 is at 2.1$\pm$0.4 kpc and G28.6+0.0 is at 9.0$\pm$0.3 kpc
from the Sun. Using published X-ray spectra of G18.9-1.1, we apply supernova
remnant models for shocked-ISM temperature and emission measure. We find that
G18.9-1.1 has a low, but not atypical, explosion energy of
$\simeq$3$\times$10$^{50}$ erg and is in a low density region of the ISM,
$\simeq$0.1 cm$^{-3}$. It has age $\simeq$3700 yr if the ejecta mass is 1.4
M$_{\odot}$, typical of Type Ia SNe, or $\simeq$4700 yr if the ejecta mass is 5
M$_{\odot}$ typical of core-collapse SN. The candidate G28.6+0.0 does not have
reported X-ray emission, so we apply a basic Sedov model. The Sedov age is
$\simeq$600 yr if the ISM density is 1 cm$^{-3}$ but could be as old as
$\simeq$6000 yr if the ISM density is as high as 100 cm$^{-3}$.
