Question

Points (4,2) and (5,1) lie on line J. what is the slope of the line that is parallel to J?

Answer 1

Two lines that are parallel have the same slope.  Thus, find the slope of the line (J) thru (4,2) and (5,1), and that will be the answer to your question.
         2-1           1
m = --------- = ------ = -1 (answer)
         4-5          -1