Answer:
44 3/8 trees per acre
Step-by-step explanation:
Let x represent the number of trees planted per acre. Let y represent the yield in bushels per tree. The farmer estimates the yield will be ...
y = 75 -4(x -70)
y = 355 -4x . . . . . . simplify
The yield per acre is this yield per tree multiplied by the number of trees per acre, x.
yield per acre = x(355 -4x) = 4(x)(88.75 -x)
This describes a downward-opening parabola with zeros at x=0 and x=88.75. The vertex (maximum) is halfway between the zeros, at x = 44.375.
To maximize her harvest, the farmer should plant 44 3/8 trees per acre. If the model is correct, each tree would then produce 177.5 bushels of fruit, almost 2.4 times the current yield.