A copper wire has radius $r=0.0250 \mathrm{~cm},$ is $3.00 \mathrm{~m}$ long, has resistivity $\rho=1.72 \cdot 10^{-8} \Omega \mathrm{m},$ and carries a current of $0.400 \mathrm{~A}$. The wire has density of charge carriers of $8.50 \cdot 10^{28}$ electrons $/ \mathrm{m}^{3}$
a) What is the resistance, $R,$ of the wire?
b) What is the electric potential difference, $\Delta V$, across the wire?
c) What is the electric field, $E$, in the wire?