For this particular problem, we use Ohm's Law. This law deals with the relation between voltage and current in an ideal conductor. It states that: Potential difference across a conductor is proportional to the current that pass through it. It is expressed as V=IR. Using the equation, we can isolate I or the current to one side and the other terms to the other side. We calculate as follows:
V = IR
I = V/R
I = 12 V / 20 Ω
I = 0.6 amperes
Therefore, the current that is flowing through the wire supplied with 12 V and having a resistance of 20 Ω would be 0.6 amperes.