Answer
$\Delta V_{total} = 5.0$ volts
Work Step by Step
We can sum the potentials of the batteries to find the overall potential difference. That is, $\Delta V_{total} = \sum_i^n\Delta V_i$
$\Delta V_1 = 3.0$ volts
$\Delta V_2 = 1.0$ volts
$\Delta V_3 = 3.0$ volts
When we sum all of the potentials, however, we must negate the second potential since it's terminals are flipped(the positive side of battery 2 is connected to the positive side of battery 1, and the negative side of battery 2 is connected to the negative side of battery 3).
$\Delta V_{total} = \Delta V_1 - \Delta V_2 + \Delta V_3 = 3.0 -1.0+3.0$
$\Delta V_{total} = 5.0$ volts
