the scale factor as I understand it will just be 1 to 30, inches to miles.
however, in this case it seems to be suggesting a conversion to the same unit, say hmmm let's convert the miles to inches.
[tex]\bf 30~\underline{mi}\cdot \cfrac{5280~\underline{ft}}{\underline{mi}}\cdot \cfrac{12~in}{\underline{ft}}\implies \cfrac{30\cdot 5280\cdot 12~in}{1}\implies 1900800~in\\\\
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\stackrel{in}{1}:\stackrel{mi}{30}\implies \stackrel{in}{1}:\stackrel{in}{1900800}[/tex]
