
Step-by-step explanation
Step 1
make the table

as we can see for every day the number of total infected is twice the previos, we can model this by the function

so, we have a pattern, that is the function

where f(x) is the total infected and x in the number of days
Step 2
the domain of a function is the set of vales x can take, in this case, we are taking x as days, so it must be greater than 0, so de domain is

the range is all values y can takes, in this case y represents the total of infected, so it must be greater or equal than 4 ( 4 people were initially infected )

I hope this helps you