Answer/Step-by-step explanation:
a. Using a point on the graph, (6, 12), and the slope of the line, we can first generate an equation in the point-slope form, given as
, where,
m = slope, and (a, b) is a point on the line.
Using two points, (6, 12) and (3, 21), let's find slope, m.

Using a point (6, 12) and slope, m = -3, generate an equation in the point-slope form by substituting a = 6, b = 12, and m = -3 in
.
✅Equation in point-slope form would be:

Rewrite this to make it be in the slope-intercept form,
.


Add 12 to both sides


✅The equation in slope-intercept form is 
b. ✍️Based on the linear model,
, the 30 represents b = y-intercept.
✅Therefore, it took Peter 30 mins long initially to deliver his package.
✍️Based on the linear model,
, "-3" represents the slope.
✅Therefore, Peter's delivery time decreased 3 mins per day.