A student investigates how the number of identical resistors connected in parallel affects the total current in a circuit. The potential difference across the parallel combination is kept constant. The table shows the student's results:
| Number of resistors | Total current in mA | Potential difference in V |
|---|---|---|
| 1 | 15.0 | 12.00 |
| 2 | 30.0 | 12.00 |
| 3 | 45.0 | 12.00 |
| 4 | 60.0 | 12.00 |
Using data from the table, calculate the resistance of only 1 resistor.