In Fig. $23-45,$ a small circular hole of radius $R=1.80 \mathrm{cm}$ has
been cut in the middle of an infinite, flat, nonconducting surface
that has uniform charge density $\sigma=4.50 \mathrm{pC} / \mathrm{m}^{2} . \mathrm{A} z$ axis, with its its
origin at the hole's center, is perpendicular to the surface. In unit-
vector notation, what is the electric ficld at point $P$ at $z=2.56 \mathrm{cm}$ ?
(Hint: See Eq. $22-26$ and use superposition.)