Solving a problem in physics, section 50, point 1 wave

1. hydrometer mass m = 0.2 kg is floating in the liquid. If you put him in a little liquid and let go, it will start to oscillate with a period T = 3.4 s. Considering undamped vibrations, find the liquid density ρ, in which floats a hydrometer. The diameter of the vertical cylindrical tube hydrometer d = 1 cm.