A p-n step junction diode with a contact potential of 0.65 V has a depletion width of 1μm at equilibrium

Q. A p-n step junction diode with a contact potential of 0.65 V has a depletion width of 1μm at equilibrium. The forward voltage (in volts, correct to two decimal places) at which this width reduces to 0.6 μm is 

Ans: 0.40 – 0.43