Think about the graph of $y = 3x^²$. Unlike most one-sided limits, this function approaches the same value from the left as it does from the right. You simply need to evaluate.

$3·(4)^² = 48$

Refer to the hint in part (a).

Think about the graph of $y=\sqrt{x}$. What happens as $x\rightarrow \infty$?
Is there a horizontal aymptote? If so, the $\lim\limits_{x\rightarrow \infty }$ will equal a constant. Or
does the function keep increasing? If so, the $\lim\limits_{x\rightarrow \infty }$ will approach $\infty$.

Refer to the hint in part (c). Note: you should be able to visualize the graph of $y=\frac{1}{x^{2}}$.