  We report simultaneous detection of twin kHz and $\sim 40$ Hz quasi-periodic
oscillations (QPOs) in the time-resolved analysis of the AstroSat/LAXPC
observation of the neutron star low mass X-ray binary, 4U 1728-34. The
frequencies of the multiple sets of triplets are correlated with each other and
are consistent with their identification as the orbital, periastron and twice
the nodal precessions frequencies. The observed relations, along with the known
spin of the neutron star, put constraints on the mass and the ratio of moment
of inertia to the mass of the neutron star to be $M^*_\odot = 1.92\pm 0.01$ and
$I_{45}/M^*_\odot = 1.07\pm 0.01$ under the simplistic assumption that the
metric is a Kerr one. We crudely estimate that the mass and moment of inertia
values obtained may differ by about 1 % and 5 %, respectively, if a
self-consistent metric is invoked. Using the TOV equations for computing the
moment of inertia of a neutron star in slow rotation approximation, having
different equations of state, we find that the predicted values of neutron star
parameters favor stiffer equations of state. We expect more stringent
constraints would be obtained using a more detailed treatment, where the
EOS-dependent metric is used to compute the expected frequencies rather than
the Kerr metric used here. The results provide insight into both the nature of
these QPOs and the neutron star interior.
