Suppose C(x) measures an economy's personal consumption expenditure and x the personal income, both in billions of dollars. Then the following function measures the economy's savings corresponding to an income of x billion dollars.

Question

S(x) = x - C(x) (Income minus consumption)
The quantity dS/dx below is called the marginal propensity to save.

For the following consumption function, find the marginal propensity to save.
C(x) = 0.701x + 99.34

$ billion per billion dollars