Question 27184
  An equation of a line is usually given in y = mx + b format.  m represents the slope of a line.  
Remember that perpendicular lines have a negative reciprocal slope.  An example of negative reciprocals are 2x and -(1/2)x.

We can say that (b) y = 4x - 4/5 and (c) y = (-) 1/4x + 4/5 are perpendicular lines.  The slope of (b) is 4x and (c) is -1/4x which are negative reciprocals of each other.