Solution :
a).
1. The domain of C(x)

Range of c(x) is

Since the negative value do not make any sense.
2. C(x) = Ax + b
Intercept here denotes the fixed cost (that is when x = 0)
The slope indicates the marginal cost (that is increase in cost per unit of quantity)
3. Revenue is maximum marginal revenue = 0
(that is when at the top of the parabola)
4. Profit = R(x) -C(x)
5. Range of P(x) is important so that we have the idea in mind about the maximum loss and the maximum profit for a particular quantity.
6 and 7 -- insufficient data.