Notice that if you just plug in [tex]x=t[/tex] into the equation for [tex]y[/tex], you end up with
[tex]\begin{cases}x=t\\y=3t^2-4\end{cases}\implies y=3x^2-4[/tex]
You have to do the same thing with the given choices. For example, if
[tex]\begin{cases}x=2t\\y=12t^2-4\end{cases}[/tex]
then we see that [tex]t=\dfrac x2[/tex], and plugging this into the second equation gives
[tex]y=12\left(\dfrac x2\right)^2-4=\dfrac{12x^2}4-4=3x^2-4[/tex]
which matches the original set of parametric equations.
So the general strategy is to eliminate the parameter [tex]t[/tex] by solving for it in each [tex]x(t)[/tex] equation. Then substitute this result for the [tex]t[/tex] in the corresponding [tex]y(t)[/tex] equation, and see if it reduces to the same equation at the top.
