Determine the current at which the battery closes with an electromotive force of 12v if, when it is closed to an external resistance

Determine the current at which the battery closes with an electromotive force of 12v if, when it is closed to an external resistance of 4 ohms, the current in the circuit is 2a.

Current I in a circuit with EMF source E, internal resistance r and external R:
I = E / r + R;
Ir + IR = E.
Internal resistance r:
r = (E-IR) / I;
Short circuit current:
Ic = E / r = E / ((E – IR) / I) = 12 V / ((12 V – 4 Ohm * 2 A) / 2 A) = 12 V / 2 Ohm = 6 A.
Answer: 6 A.