Answer:
5
Step-by-step explanation:
Number of additional trees is [tex]x[/tex]
From the question we formulate the function
[tex]f(x)=(40+x)(250-5x)\\ =-5x^2+50x+10000[/tex]
Differentiating with respect to [tex]x[/tex] we get
[tex]f'(x)=-10x+50[/tex]
Equating with zero
[tex]0=-10x+50\\\Rightarrow x=\dfrac{50}{10}\\\Rightarrow x=5[/tex]
Double derivative of the function we get
[tex]f''(x)=-10<0[/tex]
So, at [tex]x=5[/tex] the function is maximum.
So, 5 trees needs to planted per acre in order to maximize her harvest.