Question

A 12 ohm resistor is in series with an 8 ohm load. What is the total source voltage if the voltage across the 12 ohm resistor is 36 Volts?

Answer 1

The current through the resistors

$$I=\frac{V_1}{R_1}=\frac{36}{12}=3\:\rm A$$

The voltage drop across second resistor

$$V_2=IR_2=3*8=24\:\rm V$$

The total source voltage

$$V=V_1+V_2=36+24=60\:\rm V$$