Answer:
approximate length = 157.83 miles 
Explanation:
one nail = 2 inches 
5 million nails = 2(5,000,000) 
5 million nails = 10,000,000 inches 
one mile = 5280 feet 
one feet = 12 inches 
so 10,000,000/12 = 833,333.33 feet 
833,333.33/5280 = 157.828
round to nearest tenth = 157.83 
thus 5 million nails lined up together would be equivalent to 157.83 miles