R(9,0)
S(8,-4)
T(7,4)
V(6,0)
        
             
        
        
        
We can get the Profit function P(x) from the Hint.  
the Profit function is: P(x) = xp(x) - C(x) = -0.00041 x2 + 4x - 600
Attention: don't get confuse by the <span>big P of the profit with the small p of the price</span> To calculate the maximum profit, we need to find the derivative of P(x) then set it to 0 then find x: dP(x)/dx = -0.00082 x + 4 = 0 ,   so x = 4/0.00082 = 4,878 copies each month.
        
             
        
        
        
Simple interest,
FV=P(1+ni)
FV=future value=2500
P=present value, invested amount
n=number of years, =3
i=annual interest rate, =0.095
2500=P(1+3(0.095))
Solve for P.
        
             
        
        
        
6^2   = 36 is  a perfect square.