Answer
$Vs = 11.587 V $
Work Step by Step
The voltages divide in a series circuit, so the voltage of the source is just the addition of all voltages dropped in each resistance.
$Vs = 3.2 V + 5.1 V + 0.45 V + 0.03 V + 0.8 V + 0.007 V + 2 V $
$Vs = 11.587 V $
