Given data
The resistance of the first resistor is R1 = 4 ohm
The resistance of the second resistor is R2 = 5 ohm
The potential difference of the battery is V = 9 V
The resistors are connected in series. The expression for the equivalent resistance is given as:
The expression for the current in the 4-ohm resistor is given as:
Thus, the magnitude of the current flows through the 4-ohm resistor is 1 A.