y=mx+c). So the slope of the required line is -1 divided by this ie -2.
So we seek the equation of a line through (6,6) of slope -2.
This can be written:
y = -2x + c,
and as it passess through (6,6) we have:
6 = -12 + c,
so c = 18, and the equation of the line is:
y = -2x + 18.