= Solution
At fixed $N$, the <Fermi energy> scales as $E_{\mathrm F}\propto(N/V)^{2/3}$, so $\partial E_{\mathrm F}/\partial V=-(2/3)E_{\mathrm F}/V$. From $U=3NE_{\mathrm F}/5$,
$$
p=-\left(\frac{\partial U}{\partial V}\right)_N
=\frac25\frac NV E_{\mathrm F}=\frac25nE_{\mathrm F}.
$$
This is the nonrelativistic <electron degeneracy pressure>. Because $nE_{\mathrm F}\propto V^{-5/3}$,
$$
\boxed{B=-V\left(\frac{\partial p}{\partial V}\right)_{T=0,N}
=\frac53p=\frac23nE_{\mathrm F}.}
$$
The units are energy per volume, hence pressure. Converting the Fermi energies to joules gives the <ideal Fermi gas bulk modulus>
$$
\boxed{B_{\mathrm{Cu}}=6.3613\times10^{10}\ \mathrm{Pa}=63.6\ \mathrm{GPa},}
$$
$$
\boxed{B_{\mathrm{Ag}}=3.4543\times10^{10}\ \mathrm{Pa}=34.5\ \mathrm{GPa}.}
$$
These are free-electron model values. The complete mechanical bulk modulus of a real metal also involves the ionic lattice, electronic bands and interactions; the model's positive electron pressure does not by itself explain the equilibrium crystal volume.
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