$20
One loaf costs 2 dollars- Multiply both sides of the ratio by 10 and you get 20 as ur answer.
Since it is perpendicular to y=3x-1, the slope must be a negative reciprocal.
there the slope of the perpendicular line is

So now we have,

To find b, we use the point that the line passes through and substitute it to the y and x values.

which would give us b=5/3
Therefore, the equation of the line is
2/5-1/4
8/20 - 5/20
(8-5)/20
= 3/20
I hope that's help ! if you have question please ask