Answer
$y=1-\dfrac{x^3}{8}$
Work Step by Step
Given the graph of $y=f(x)$ and a real number $c>1$, we obtain the graph of $y=f(\dfrac{x}{c})$ by horizontally stretching the graph of $y=f(x)$ by a factor of $c$.
Hence to horizontally stretch the graph of $y=1-x^3$ by a factor of 2, we replace each occurrence of $x$ in this equation by $\dfrac{x}{2}$, and, thus, obtaining the equation $$y=1-\dfrac{x^3}{(2)^3},$$ or equivalently, $$y=1-\dfrac{x^3}8.$$
