To find the unit rate of growth of the tree in feet per year, we can start by solving for \( t \) in the equation \( 20t = 860 \).
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Divide both sides of the equation by 20: \[ t = \frac{860}{20} \]
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Now, calculate \( \frac{860}{20} \): \[ t = 43 \]
This means the tree is 43 years old. Since the tree has grown 860 feet in 43 years, we can find the annual growth rate (the unit rate) by dividing the total height of the tree by its age:
\[ \text{Unit rate} = \frac{860 \text{ feet}}{43 \text{ years}} = 20 \text{ feet per year} \]
Thus, the unit rate in the equation is:
A. 20 feet per year.
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