The length of AC is 4 miles, the correct option is B.
What are Similar Triangles?
Two triangles of the same shape are called similar if their sides are in proportion.
The triangle ΔABC and ΔCDE are similar
when triangles are similar their sides are in proportion
Let x be the length of AC
21 ft / 7 miles = 12 ft /x miles
x = 4 miles
Therefore, the length of AC is 4 miles, the correct option is B.
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