A 9.0 ohm and a 6.0 ohm resistor are connected in series with a power supply. (A) the voltage drop across the 6.0 ohm resistor is measured to be 12 V. find the voltage output of the power supply. (B) the two resistors are connected in parallel across a power supply, and the current through the 9.0 ohm resistor is found to be 0.25 A. find the voltage setting of the power supply?