Answer:
(a) y = (-5/4)x +(17 1/2)
(b) 17 1/2 hours the first day, decreasing by 1 hour 15 minutes per day
Step-by-step explanation:
(a) The line on the graph goes through two points that are on grid lines, so it is convenient to use those points to determine the equation of the line. The 2-point form of the equation of a line is convenient for the purpose.
The points are (2, 15) and (6, 10).
The 2-point form of the equation is ...
y = (y2 -y1)/(x2 -x1)·(x -x1) +y1
Filling in the points we chose, this becomes ...
y = (10 -15)/(6 -2)·(x -2) +15
y = (-5/4)(x -2) +15
y = (-5/4)x +(17 1/2)
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(b) Setup time on Day 0 is the value of y when x=0: 17 1/2 hours.
The slope of the line gives the change per day: a decrease of 5/4 hours, or 1 hour 15 minutes.
