Answer:
E = {(Charge Density/2e0)*(1 - [z/(sqrt(z^2 - R^2))]}
R is radius = Diameter/2 = 0.210m.
At z = 0.2m,
Put z = 0.2m, and charge density = 2.92 x 10^-2C/m2, and constant value e0 in the equation,
E can be calculated at distance 0.2m away from the centre of the disk.
Put z = 0.3m and all other values in the equation,
E can be calculated at distance 0.3m away from the centre of the disk