Answer
$$ p=\pm .5i$$
Work Step by Step
For imaginary numbers, we know that standard form is $a\pm bi$, where $a$ is the real part and $b$ is the imaginary part. To get the expression into this form, we combine like terms like we did with polynomials. Doing this, we find:
$$12p^2 = -3 \\ p =\sqrt{-\frac{1}{4}} \\ p=\pm .5i$$