Find an equation of the line L, where L is perpendicular to y=3x and passes through the point (1,3)

Question

I know the slope would be -1\3x

but in my answer keyy it says the answer is -1\3x + 10/3 I am not sure how they got the +10\3 part

thanks

Answer 1

You have a slope and a point, so

y-3 = -1/3 (x-1)

Now all should be clear.