In which of the resistors in the circuit below is the power dissipated the least?

Two long parallel wires carry equal currents in opposite directions. What field do the two wires produce at point M, which is midway between the wires and on the plane of the paper?

A student assigns currents at a junction in a circuit as shown in the diagram.

The student's calculations correctly give that $I_1=3 \mathrm{A}$ and  $I_2=-2 \mathrm{A}$. The value of $I_3$ is: