**Hint:**

Start by understanding Ohm's law, which is V = IR, where V is voltage, I is current, and R is resistance.

In this problem, you need to find the maximum current drawn from the battery, but you have both the emf of the battery (E) and its internal resistance (r).

Remember that when calculating the maximum current, you need to consider the total resistance in the circuit.

**Step-by-Step Solution:**

Recall Ohm's law: V = IR, where V is the voltage (emf of the battery), I is the current, and R is the total resistance.

The total resistance in the circuit is the sum of the internal resistance (r) of the battery and the external load resistance (R): $R_{\text{total}} = r + R$.

To find the maximum current (I), we need to determine the value of R that minimizes the total resistance R_total.

Use the formula $I = \dfrac{E}{R_{\text{total}}}$, where E is the emf of the battery.

Substitute the given values: E = 12 V and r = 0.4 Ω.

Solve for the maximum current (I). The result will give you the maximum current drawn from the battery when the load resistance is optimized for maximum current flow.

**Note:** The maximum current drawn from a battery depends not only on the emf (voltage) of the battery but also on the internal resistance of the battery and the resistance of the external load. It's essential to minimize the total resistance in the circuit to achieve the maximum current. In practice, this may involve choosing an external load that matches the internal resistance to maximize current output. In this specific problem, the maximum current drawn from the given battery is 30 A when the load resistance is adjusted accordingly.