AP EAMCET Engineering 2018 Apr 22 Shift 2 Paper

One plate of a parallel plate capacitor is connected to a spring as shown in the figure. The area of each plate of the capacitor is A and the distance between the plates is d when the battery is not connected and the spring is unstretched. After connecting the battery, in the steady state, the distance between the plates is 0.74d, then the force constant of the spring is