Hartzell Inc. had the following data for $2020,$ in millions: Net income $=$ $$600$; after$-$tax operating income $[$EBIT$(1-$ T$)]=$ $$700$; and Total assets $=$ $$1,700.$ Information for $2021$ is as follows: Net income $=$ $$825$; after$-$tax operating income $[$EBIT$(1-$ T$)]=$ $$1,100$; and Total assets $=$ $$2,250.$ Assume the firm had no excess cash. How much free cash flow did the firm generate during $2021?$

a$.$ $$275$ million

b$.$ $$1,375$ million

c$.$ $$1,650$ million

d$.$ $$550$ million

e$.$ $$875$ million