Write an equation of a line that is perpendicular to the line y=3x-6 and goes through the point (-3,5)

plz help me ...and explain how to do

The slope of the line y=3x-6 is 3. A perpendicualr line will have to have slope -1/3, because the product of the two slopes must be -1. A proof or statement of that should be in your textbook.

The line you want must have the form
y = (-x/3) + b, where b is a constant you can figure out by requiring that y = 5 when x = -3.

5 = (-(-3)/3) + a = a + 1
a = 4.

Therefore the line you want is

y = (-x/3) + 4