Explanation:
Line y = 3x +2 you should recognize, is in form y = mx + b.
where 'm' is the slope = 3
now you should have been told, and you have to remember ( i.e. - learn) that the PERPENDICULAR slope to this is - 1/m
for this case, that would be - 1/3
so your new line begins to look like this: y = - 1/3 x + b
Now, substitute in the point 3,5 so you can compute the value of 'b'
5 = -1/3 (3 ) + b shows b = 6
your new line is then y = -1/3 x + 6