If you divide the equation for the given line by 2, it will be in slope-intercept form:
y = (1/3)x +7
This tells you its slope is 1/3. The slope of the perpendicular line is the negative reciprocal of this: -1/(1/3) = -3. The point-slope form of the equation for the perpendicular line can be written as ...
y = m(x -h) +k . . . . . line with slope m through point (h, k)