first you want to get it into standard form. which would mean you get the x of the side of the y and divide everything by the y's coefficient in this case 3.
3y-x=a
3y=x+a
y=1/3x+a
Now your going to want to turn this into a perpendicular li e which means you flip the coefficient and make it negitive
y=-3x+a
then we fill in the points.
-1=-3(2)+a
Solve
-1=-6+a
-1+6=a
5=a
Now put it in standard form.
y=-3x+5
