Define the functions $F(x)$ and $G(x)$ by
$$F(x) = \int_{-x}^{x} t^3 dt , \quad G(x) = \int_{-x+6}^{x+6} t^3 dt$$
Determine whether each of the following improper integrals and limits is divergent or convergent. If it is convergent, evaluate it. If it diverges to infinity, state your answer as "INF" (without the quotation marks). If it diverges to negative infinity, state your answer as "MINF". If it diverges without being infinity or negative infinity, state your answer as "DIV".
(a) $$\int_{-\infty}^{\infty} x^3 dx$$

(b) $$\lim_{x\rightarrow\infty} F(x)$$

(c) $$\lim_{x\rightarrow\infty} G(x)$$