we have that
The dimensions of the originally draw are [tex]3\ in\ x\ 5\ in[/tex]
we know that
If the two drawings are similar
then
the ratio of the corresponding sides are equals
so
[tex]\frac{10.5}{5}= \frac{x}{3} \\ \\5x=10.5*3 \\ \\x=6.3\ in[/tex]
therefore
the answer is
the length of the other dimension is [tex]6.3\ in[/tex]