A. by how much will gdp change if firms increase their investment by $11 billion and the mpc is 0.9?

The answer is "$110 billion".

Explanation:

Firms increase their investment by $11 billion

mpc = 0.9

gdp = ?

To find the gdp, first we have to find expenditure multiplier;

we will find that by using the formula;

expenditure multiplier = 1 / (1-0.9) = 1/0.1 = 10

Now gdp = 10 x $11 billion

= $110 billion

Thus the gdp is $110 billion.