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Quasi-periodic oscillations (QPOs) observed in giant flare from the magnetar, which is a strongly magnetized neutron star, are crucial information for extracting the neutron star properties. To theoretically explain the QPOs newly observed in GRB 200415A, we systematically examine the crustal torsional oscillations. Then, we find that the observed QPOs can be identified with several overtones of crustal oscillations, if the value of the combination of the nuclear saturation parameters, ς, is well-selected, depending on the neutron star mass and radius. Thus, we can inversely constrain the neutron star mass and radius for GRB 200415A by comparing to the appropriate range of ς expected with the fiducial value of nuclear saturation parameters obtained from the terrestrial experiments. We further make the neutron star mass and radius constraint more severe by assuming that the neutron star radius is almost the same as that for the neutron star model, whose central density is twice the nuclear saturation density. The resultant neutron star models are consistent with the constraints obtained from the other astronomical and experimental observations.