In the circuit shown in Fig. all meters are idealized and the batteries have no appreciable internal

Question:

In the circuit shown in Fig. all meters are idealized and the batteries have no appreciable internal resistance.
(a) Find the reading of the voltmeter with the switch S open. Which point is at a higher potential: a or b?
(b) With the switch closed, find the reading of the voltmeter and the ammeter. Which way (up or down) does the current flow through the switch?