The answer is D. The relative minimum and maximums are where they kind of curve and come back up or down. So that is 64 and -36.
The actual trees should be planted 43 ft apart
ANSWER
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EXPLANATION
We want to find the slope of a line that is perpendicular to the line y = 1
The line y=1 is parallel to the x-axis.
In other words, the line y=1 is a horizontal line.
The line perpendicular to y=1 is a vertical line.
The slope of a vertical line is undefined