  In this third paper of a series, we study the kinematics of the ionised gas
and stars, calculating the dynamical masses of the circumnuclear star-forming
regions in the ring of of the face-on spiral NGC 7742. We have used high
spectral resolution data from the MEGARA instrument attached to the Gran
Telescopio Canarias (GTC) to measure the kinematical components of the nebular
emission lines of selected HII regions and the stellar velocity dispersions
from the CaT absorption lines that allow the derivation of the associated
cluster virialized masses. The emission line profiles show two different
kinematical components: a narrow one with velocity dispersion $\sim$ 10 km/s
and a broad one with velocity dispersion similar to those found for the stellar
absorption lines. The derived star cluster dynamical masses range from 2.5
$\times$ 10$^6$ to 10.0 $\times$ 10$^7$ M$_\odot$. The comparison of gas and
stellar velocity dispersions suggests a scenario where the clusters have formed
simultaneously in a first star formation episode with a fraction of the stellar
evolution feedback remaining trapped in the cluster, subject to the same
gravitational potential as the cluster stars. Between 0.15 and 7.07 % of the
total dynamical mass of the cluster would have cooled down and formed a new,
younger, population of stars, responsible for the ionisation of the gas
currently observed.
