Answer
a) $-9.27\times10^{-24}\,J/T$
b) $1.85\times10^{-23}\,J/T$
Work Step by Step
Recall that the z-component of the orbital magnetic dipole moment $\mu_{orb,z}=-m_{l}\mu_{B}$ where $\mu_{B}$(Bohr magneton)=$9.27\times10^{-24}\,J/T$.
a) When $m_{l}=1$, $\mu_{orb,z}=-1\times9.27\times10^{-24}\,J/T$
$=-9.27\times10^{-24}\,J/T$
b) When $m_{l}=-2$, $\mu_{orb,z}=-(-2)\times9.27\times10^{-24}\,J/T$
$=1.85\times10^{-23}\,J/T$
