(a).

The general linear function is .

is the total cost of the function in dollars

is the number of minutes used.

is the domestic long distance package.

Fixed cost is $.

Cost per minute $ per minute.

Total cost : .

The function is .

(b).

Find the cost of talking for milnutes and minutes.

Substitute in the function .

The cost of talking is $ for minutes. 

Substitute  in the function .

The cost of talking  is $ is minutes.

(a)

The function is .

(b)

The cost of talking is $ for  minutes. 

The cost of talking  is $ is minutes.