Answer
The weight of Robert Wadlow before his death was $607\ \text{lb}$.
Work Step by Step
The height of Robert before his death was $107\text{ inches}$ and a man with the same body type will have a height of $70\text{ inches}$ and a weight of $170$ pounds.
According to the question,
$\begin{align}
& w\propto {{h}^{3}} \\
& \text{or} \\
& w=k{{h}^{3}} \\
\end{align}$
Now, if the height $h=70\text{ inches}$ and the weight $w=170\text{ lb}$ then,
$\begin{align}
& w=k{{h}^{3}} \\
& 170=k{{(70)}^{3}} \\
& 170=k(343000) \\
& k=\frac{170}{343000}
\end{align}$
Hence, $k=0.000496$.
Now let us calculate Robert’s weight,
$\begin{align}
& w=0.000496{{h}^{3}} \\
& w=0.000496{{(107)}^{3}} \\
& \ \ \ =0.000496(1225043) \\
& \ \ \ \approx 607\ pounds
\end{align}$
