Peter bought 90 boards for $270.
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Answer:
You can see the graph below.
To answer the question, you need to draw a vertical line from x = 12h up, until the line meets with the line.
Once the line meets with the line, draw a horizontal line from that point, and the value where this line intersects with the y-axis will be the distance from home after 12 hours.
The graph is kinda hard to read because the line is really steep, the green line is the equation y = 40*x
the red line is a line at x = 12
The black dashed line is the horizontal line that intersects with the y-axis.
In the graph, you can see that the dashed line intersects the y-axis at around y = 475.
Then a good estimate is that the distance after 12 hours is 475 (miles).
Now, we can compare this with the direct calculation, just replace x by 12 in the given line:
y = 40*12 = 480.
So our estimation is really accurate.
