Question 150713
In order to two lines to be paralle, they need to have the same slope. Generally slope is assigned to a variable named "m". In this problem the points are using m in them, so use a different variable for slope.

slope using the first two points
{{{s = (y[2] - y[1])/(x[2] - x[1])}}}
{{{s = (1-m)/(2 - (-8))}}}
{{{s = (1-m)/10}}}



slope using the second two points
{{{s = (y[2] - y[1])/(x[2] - x[1])}}}
{{{s = (m+1 - 1 )/(7 - 11)}}}
{{{s = m/(-4)}}}


Now set the two slopes equal
{{{(1-m)/10 = -m/4}}}
{{{1-m = -5m/2}}}
{{{2 - 2m = -5m}}}
{{{2 = -3m}}}
{{{-2/3 = m}}}