Answer
The rational expression is proper.
Work Step by Step
A rational expression $\dfrac{A(x)}{B(x)}$ is said to be proper if the degree of polynomial in numerator is less than the degree of its denominator.
Here, the degree of the numerator $A(x)= 5x+2$ is $1$ and the degree of the denominator ; $B(x)=x^3-1$ is $3$.
Since $1< 3$, then the given rational expression is proper.