The velocity of the mass center of a rigid body of mass \(3 \mathrm{~kg}\) undergoing planar motion is \((3 \mathbf{i}+4 \mathbf{j}) \mathrm{m} / \mathrm{s}\). The mass center is \(20 \mathrm{~cm}\) from the fixed axis of rotation. Calculate the angular velocity of the body at this instant.