Answer
a. 0.468 T.
b. Three levels.
Work Step by Step
Apply the formula $\Delta U = \mu_B B$.
$$B=\frac{\Delta U}{\mu_B}=\frac{2.71\times10^{-5}eV}{5.79\times10^{-5}eV/T}=0.468T$$
b. For a 3p state, $l=1$. There are 3 levels, because for $l=1$, $m_l$ has 3 values: -1, 0, and +1.
