Simple Harmonic Motion

The upper end of the spring is fixed and a mass '\(m\)' is attached to its lower end. When mass is slightly pulled down and released, it oscillates with time period 3 second. If mass '\(\mathrm{m}\)' is increased by \(1 \mathrm{~kg}\), the time period becomes 5 second. The value of '\(\mathrm{m}\)' is (mass of spring is negligible)