Let’s see if I can help you :)!
With two points you can define a line.
So, the line parallel to s is q, which has these two pointS: (3,6) and (6,3)
There are different ways to get the line. For instance, this one:
Y = a*x+b
a = slope = difference_y/difference_x = (3-6)/(6-3) = -1,
y = -x + b,
Now use any point, say (3,6) to get b:
6 = -3+b-> b - 9.
Line is y = -x + 9,
It checks out in the other point: (6,3) —> 3 = -6+9 = 3. Good.
Other method:
y-y2 = a*(x-x2), where (x2,y2) is one of the two points and a is the slope as defined before.
Really hope this helped you!