How many square miles are in 12 miles?

Answer 1

None, since there can be no conversion. A mile is a measure of length in 1-dimensional space while a square mile is a measure of area in 2-dimensional space. The two measure different characteristics and, according to the most basic principles of dimensional analysis, any attempt at comparisons or conversions between the two are fundamentally flawed.

Answer 2

Miles are a measure of distance, and square miles are a measure of area. You can't convert a distance measurement to an area measurement.