Answer:
m [slope] = 1/12
Explanation:
If a line is perpendicular (90 degrees, forms a right angle) to another, the slope of the line must be an opposite reciprocal of the other. The opposite reciprocal of m is -1/m.
An opposite reciprocal is created by flipping the numerator and denominator, and making it negative.
Therefore, if m is -12 it's opposite reciprocal is -1/-12 = 1/12.