You can put this solution on YOUR website!
Y=mX+b WHERE (M)=SLOPE & (b)=Y INTERCEPT.
TO FIND A LINE PERPENDICULAR TO THE LINE Y=X+7 IS -1.
NOW REPLACE X BY 3 & Y BY 6 AND SOLVE FOR THE Y INTERCEPT(b). THUS:
b=9 Y INTERCEPT.
thus the equation for this line is y=-x+9 [the green line]
Y=X+7 [the red line]
(graph 300x300 pixels, x from -10 to 10, y from -10 to 10, y = x +7 and y = -x +9).