Using the information given, it is found that:
A linear function is modeled by:
[tex]y = mx + b[/tex]
In which:
Item a:
The slope is given by the change in y(total bill) divided by the change in x(number of days), hence:
[tex]m = \frac{506 - 338}{19 - 12} = 24[/tex]
The slope is of 24, which means that for each day, the total bill increases by $24.
Item b:
[tex]y = 24x + b[/tex]
[tex]338 = 24(12) + b[/tex]
[tex]b = 50[/tex]
Hence, the linear equation is: [tex]y = 24x + 50[/tex]
You can learn more about linear functions at https://brainly.com/question/25823744