Answer
$\Delta V_{34} = -140~V$
Work Step by Step
We can find $\Delta V_{34}$:
$\Delta V_{34} = \Delta V_4 - \Delta V_3$
$\Delta V_{34} = (\Delta V_4 - \Delta V_1)+(\Delta V_1 - \Delta V_2)+(\Delta V_2 - \Delta V_3)$
$\Delta V_{34} = \Delta V_{14}+\Delta V_{21}+\Delta V_{32}$
$\Delta V_{34} = (-60~V)+(-30~V)+(-50~V)$
$\Delta V_{34} = -140~V$
