Answer
Fill the blanks with
a. $\infty$ and $-\infty$
b. $-\infty$ and $-\infty$
Work Step by Step
a. The leading power has an odd exponent $(3)$.
(very large negative number$)^{odd}$ is a very large negative number
(very large positive number$)^{odd}$ is a very large positive number
The coefficient is $+1$ (positive) preserving the sign, so
$ y\rightarrow-\infty$ as $ x\rightarrow-\infty, \qquad y\rightarrow+\infty$ as $ x\rightarrow+\infty$
b. The leading power has an even exponent (4).
(very large negative number$)^{even}$ is a very large POSITIVE number
(very large positive number$)^{even}$ is a very large positive number
The coefficient is $-1$ (negative), changing the sign, so
$ y\rightarrow-\infty$ as $ x\rightarrow-\infty, \qquad y\rightarrow-\infty$ as $ x\rightarrow+\infty$
