Find the current through the 30.0 ω resistor.

To calculate for the current, we simply have to take the ratio of the voltage over resistance. That is:

Current, I = Voltage, V / Resistance, R

I = V / R

So for example if our voltage is 12.5 V and our resistance is 30.0 ohms, current is:

I = 12.5 / 30

I = 0.417 A = 417 mA