If a family's MPC is .7, it is:
a. operating at the break-even point
b. spending seven-tenths of any increment to its income.
c. Necessarily disaving
d. spening 70 percent of its income on consumer goods.

Hello.

The answer is "b."

The "fraction of additional income that people spend has a special
name, the marginal propensity to consume (or mpc for short)."  If "the
mpc is... three-fourths" and "income increases by $8000... people
increase spending by $6,000"
source: The Simple Keynesian Model, hosted by saintjoe.edu
http://ingrimayne.saintjoe.edu/econ/Keynes/SimpleModel.html

search strategy: "marginal propensity to consume", spends

I hope this helps.