According to the sustainable growth model, if a firm finances its assets with 75% debt and 25% equity, and retains $3 million in earnings in a given year, the firm can afford to borrow an additional ______ to maintain the desired mix of debt and equity.
a. $9 million
b. $5.25 million
c. $2.25 million
d. $1 million
e. $500,000
f. $450,000
g. none of the above