The canonical linear equation of the line ( slope-intercept) is :
y = mx + b
where m is the slope and b is the coordinate y of the y-intercept.
Now from the statement of the problem we know that the slope m = -2, then the canonical lineal equation of the line would be:
y = -2x + b
The only thing we need to find is the y-intercept. Take the point (x,y) = (-7,6) and replace it in the above equation:
6 = -2(-7) + b
this is equivalent to say:
6 = 14 + b
solve for b
b = 6-14 =-8
then we can conclude that the linear equation is :
y = -2x -8