Answer:
9 1/2 inches
Explanation:
The scale of a map is the ratio of map distance to represented distance. This can be used to write a proportion.
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map distance/represented distance = 1 in/(30 mi) = x/(285 mi)
where x represents the map length of the southern border.
Multiplying by 285 mi, we have ...
x = (285 mi)(1 in)/(30 mi) = 9.5 in
The border is 9.5 inches on the map.