SOLUTION
We are trying to get the equation for the horizontal line passing through the point (-6,-6).
( x1 , y 1 ) = ( 0, 0 )
( x2 , y2 ) = ( -6 , -6 )
Gradient, m = ( y2 - y1 ) / ( x2 - x1 )
m = ( -6 -0 ) / ( -6 - 0 )
m = -6 / - 6
m = 1
Then, using the equation of a line;
y - y 1 = m ( x - x 1 )
y - 0 = 1 ( x - 0 )
y = x
