Final answer:
In a series circuit, the voltage across each component is the same as the voltage across the battery.
Step-by-step explanation:
In a series circuit, the voltage across each component is the same as the voltage across the battery. So in this case, the voltage across the battery is 12V.
We can find the voltage across the resistor by using Ohm's Law. Ohm's Law states that V = I x R, where V is the voltage, I is the current, and R is the resistance.
We are given the current and resistance of the resistor, so we can calculate the voltage using the formula.
V = I x R = 4A x 3Ω = 12V