Question

WHEN SIX PEOPLE WHOSE AVERAGE MASS IS 84 KG SIT DOWN IN A CAR, THEY FIND THAT THE CAR DROPS .84 CM LOWER ON ITS SPRINGS. THEN THEY HAVE GET OUT OF THE CAR AND BOUNCE IT UP AND DOWN. THE ACCELERATION OF GRAVITY IS 9.8 M/S^2. WHAT IS THE FREQUENCY OF THE CAR'S VIBRATION IF ITS MASS (EMPTY) IS 1300 KG? ANSWER IN UNITS OF HZ