Question

I don't remember how to do this.

Answer 1

So the equation of a line is:
y = mx + b

You are given an x and a y and a rate, which is the slope of the line (m).
The rate is given as N per unit.  This means the 'unit' whatever it is referring to will be your 'x' variable.

Then solve for y-intercept (b) by subbing in your x,y values.
----> b = y - mx

Example 3:
Rate is $8 per day.  Days are my x variable, Dollars are my y variable.
Given:  x = 3, y = 29

b = y - mx = 29 - (8)(3) = 29 - 24 = 5

Equation of line:
y = 8x + 5

Hope this helps