Use Norton's theorem to solve for $I_3$ in Figs. $10-68$ and $10-69.$ Draw the Norton equivalent of each circuit to which $R_L$ is connected. $($Hint: When A to B is shorted, the sources produce current flow independent of each other. The short$-$circuit current $I_N$ is the algebraic sum of the source currents. Consider currents flowing from top to bottom through shortcircuited terminals A and B as negative, and currents from bottom to top as positive.$)$