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$)]=$ $$1,050$; and Total assets $=$ $$2,200.$ Assume the firm had no excess cash. How much free cash flow did the firm generate during $2021?$

a$.$ $$1,325$ million

b$.$ $$325$ million

c$.$ $$550$ million

d$.$ $$825$ million

e$.$ $$1,550$ million