Hartzell Inc. had the following data for $2020,$ in millions: Net income $=$ $$600$; after$-$tax operating income $[$EBIT$(1-$ T$)]=$ $$700$; and Total assets $=$ $$2,200.$ Information for $2021$ is as follows: Net income $=$ $$825$; after$-$tax operating income $[$EBIT$(1-$ T$)]=$ $$975$; and Total assets $=$ $$2,800.$ Assume the firm had no excess cash. How much free cash flow did the firm generate during $2021?$

a$.$ $$375$ million

b$.$ $$225$ million

c$.$ $$1,575$ million

d$.$ $$750$ million

e$.$ $$1,425$ million