Calculate the electrical resistance of the resistor, when connected to a DC

Calculate the electrical resistance of the resistor, when connected to a DC source with an EMF of 6 V and an internal resistance of 1 Ohm, the current in the circuit will be 2 A.

Ohm’s law is valid for a complete chain:
I = E / (R + r), where
I – current in the circuit,
E – source EMF,
R – resistance of the external section of the circuit,
r is the internal resistance of the source.

Substitute the values from the condition:
2 A = 6 V / (R + 1 Ohm);
(R + 1 Ohm) * 2 A = 6 V;
R + 1 Ohm = 6 V / 2 A;
R = 3 Ohm – 1 Ohm = 2 Ohm.

Answer: 2 ohms.