Answer
The sheet must be 4 x 100'099'511'628 inches.
Work Step by Step
The short side is easy to calculate: $\frac{10 u}{1 in}=\frac{40 u}{n}$, just have to divide the number of units by 10
$n=4$ inches
But to the length of the other side is $\frac{20^{40}}{10}$ which is an insane $100'099'511'628$ inches or, for those who are curious, about $1'579'853$ miles.
