First, you need to find the slope of this new line.
It is perpendicular to the given line, which means the slope of this line is the negative reciprocal of this given line, so we need to find out the slope of the equation 3y=6x+3
divide each side by 3, you'll get y=2x+1, so we know the slope is 2, which is 2/1
the slope for the new line should be -1/2, the negative reciprocal of 1/2
Next, use point-slope format to write your equation. Your point is (2,4) and your slope is -1/2, so you have
(y-4)=-1/2(x-2)
If you want to simplify it: y-4=-1/2x+1 => y=(-1/2)x+5