Well for starters, your line is , which becomes , and so its gradient is 3, not -3. Therefore the perpendicular line should have gradient .
Use the distance from a point to a line formula to check the distance from P(7, -4) to 3x - y =5
okay the slope of the line is -3/1, which is perpendicular to 1/3
so the equation i think is y+4/x-7
which ive then written 3(y+4)=1(x-7)
then 3y+12 = x-7
and i wrote x +3y = 19,
i'm not sure if what i just wrote was correct, and i don't know where to go from there..