For a spring we have the frequency angular frequency W^2 = k/m where m is the mass on the spring and k is the spring constant.
When a mass of 0.85 kg is attached to the spring the frequency is 1.43 Hz.
=> 1.43^2 = k/(0.85)
To find the change in frequency for a change in mass, we have to use the value of k which can be derived from the equation given above.
k = 1.43^2*0.85
For an increase in mass of 0.32 kg:
W = sqrt [1.43^2*0.85/(0.85 + 0.32)]
=> 1.218 Hz
For a decrease in mass of 0.32 kg:
W = sqrt [1.43^2*0.85/(0.85 - 0.32)]
=> 1.810 Hz