Here are the equations of 5 straight lines. P: y = 2x+5 Q: y = -2x+5 R: y = x+5 S: y = -1/2x+6 T: y = 1/2x+1 (a) Write down the letter of the line that is parallel to y=x+6 (b) Write down the letter of the line that is perpendicular to y = 2x - 1 ​