Question 119052
The starting point or y-intercept is 27 feet.  The slope is -1 1/2 or -3/2 feet.  The slope is negative since the water level is falling.  The y-value is the number of feet at a particular week.  The x-value = the number of weeks.

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Using the slope-intercept form of a line: y=mx+b
The equation of this line is: y={{{((-3/2)x+27)}}}
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Let y=18 feet
18={{{((-3/2)x+27)}}} [solve for the x=value]
x=6 weeks
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So within 6 weeks, the water level will at 18 feet.
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