We have two resistors in parallel, so we can use the formula for parallel resistors:
$$\frac{1}{R_{eq}} = \frac{1}{R_1} + \frac{1}{R_2}$$
Here, $R_1 = 4.00\,\Omega$ and $R_2 = 12.0\,\Omega$. Plugging in the values, we get:
$$\frac{1}{R_{eq}} = \frac{1}{4.00} +
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