Answer
d. investment will increase from ${$25}$ billion to ${$30}$ billion.
Work Step by Step
When the real interest rate is 6%, the investment will be ${$25}$ billion, and when the real interest rate is 4%, the investment will be ${$30}$ billion, an increase of ${$5}$ billion, from ${$25}$ to ${$30}$ billion, leading to choice (d).
