The circuit shown in Fig, 25.37 contains two batteries, each with an emf and an internal resistance, and two resistors. Find (a) the current in the circuit (magnitude and direction); (b) the terminal voltage $V_{a b}$ of the $16.0-\mathrm{V}$ battery; (c) the potential difference $V_{e c}$ of point $a$ with respect to point $c .$ (d) Using Fig. 25.21 as a model, graph the potential rises and drops in this circuit.