stupid calculus

[Guest]

The consumption function of an economy is as follows, where C(x) is the personal consumption expenditure and x is the personal income, both measured in billions of dollars.
C(x) = 0.644x + 83.61
Find the rate of change of consumption with respect to income, dC/dx. This quantity is called the marginal propensity to consume.

[Guest]

AB+CD=149

Find all possible answers of A, B, C & D.

[Guest]

dC/dx = 0.644

[HallsofIvy]

I suppose it would be churlish of me to point out that it was not the "Calculus" that was stupid!
Have you ever actually taken a Calculus course? I would expect the derivative of such a function to be covered in the first few weeks.