Answer
See explanation.
Work Step by Step
Equation 27.19 tells us the magnetic force on a current-carrying wire, $\vec{F}=I\vec{l}\times \vec{B}$. The direction depends on both the current’s direction $\vec{l}$ and the magnetic field $\vec{B}$. We should orient the straight-line current in different directions, and note the direction of the force in every case.
There will be only one direction for the magnetic field $\vec{B}$ that is consistent with the right hand rule and the directions of the current and of the magnetic force.
