Solution (source code)

= Solution

The initial and final slopes from part (i) are $(1+\alpha)^{-1/3}$ and $(1+\alpha)^{-1/2}$. The prescribed ratio gives
$$
(1+\alpha)^{-1/2}=\frac12(1+\alpha)^{-1/3}
\quad\Longleftrightarrow\quad
(1+\alpha)^{1/6}=2.
$$
Consequently
$$
\boxed{\alpha=63}.
$$