If the arrow had been drawn the other way, we would get a negative current. A negative current going to the right is equivalent to a positive current going to the left. Further, with a positive conventional current, the voltage across a resistor will be positive on the end the current enters and negative on the end the current leaves. The only reason it's not exactly zero volts is due to rounding errors in our calculations. A, we can start at ground on the left side of figure 5.
Ground is zero volts.
We go up an additional 172.4 mV as we go through R12, since we are also coming out the positive side of R12. This makes V A 5.1724 volts. We could have determined V A starting below the right voltage source. The minor difference is, again, due to rounding. We have a couple ways of finding V B .