Final answer:
To maximize the harvest, the farmer should plant 60 trees per acre.
Step-by-step explanation:
Let's assume x is the number of additional trees planted per acre.
The total number of trees planted per acre when x additional trees are planted is 60 + x.
The yield per tree when x additional trees are planted is given by the equation 45 - 4x.
To maximize the harvest, we need to find the value of x that maximizes the yield per acre.
The yield per acre is calculated by multiplying the number of trees planted per acre with the yield per tree:
Yield per acre = (60 + x) * (45 - 4x)
To find the maximum value of the yield per acre, we take the derivative of the equation and set it equal to zero:
(60 + x)(-4) + (45 - 4x)(1) = 0
-240 - 4x + 45 - 4x = 0
-8x - 195 = 0
-8x = 195
x ≈ -24.375
Since the number of trees planted cannot be negative, we round x down to the nearest whole number:
x = -24
Therefore, the farmer should plant 60 trees per acre to maximize her harvest.