Finding voltage in series-parallel
Contrast to the other two answers, I think the most obvious way to answer this question is to simply use KVL. If the switch is closed, then you know the voltage across \$R_4\$ is the same as the voltage across \$R_2\$ and \$R_3\$ (due to the definition of a wire in a schematic). This is confirmed by the given information (\$1.2V + 1.2V = 2.4V\$). Following this, you simply add the given voltage across \$R_1\$ and the resulting voltage is the voltage across the battery.