Statement reason 1. δabc and δdef are similar. given 2. property of similar triangles 3. property of proportion 4. slope of line ac: definition of slope 5. slope of line df: definition of slope 6. substitution property of equality 8 the table contains the proof of the theorem of the relationship between slopes of parallel lines. what is the missing statement for step 6? a. b. c. d. e. its important.