I'd use synthetic div. here, with 2 as my divisor:
________________
2 / 1 -11 18
2 -18
----------------------------
1 -9 0
Note that the coefficients of the missing factor are given here and are 1 and -9. Thus, (x-9) is the missing factor.
A) 3x (you substitute the g equation into the f one by putting it in the x value for f)
b) x (do the same thing, but switch the letters)
Marginal profit, P(x) = R(x) - C(x)
P(x) = x³ - 5x² + 7x + 10
x³ - 5x² + 7x + 10 = 0
If you solve it, you get x = -0.839 where P(x) is zero
324 is the answer to your promblem welcome