Ohm's law.
The intensity of current through a circuit is directly proportional to the voltage or voltage of the same and inversely proportional to the resistance it presents.

In the form of a fraction, it is put in the following way:

I equals V among R.

Where I is the intensity that is measured in amperes (A), V the voltage that is measured in volts (V); and R the resistance that is measured in ohms (Ω).

With this expression you will be able to calculate a magnitude in one circuit from the other two. To calculate the intensity, we directly calculate the previous fraction.