2. Linear models occur frequently in real settings not accompanied by data. For each of the described setting, give a formula for the corresponding linear model.

a. A calling card offers a price of $0.21 cents per minute at any time during the day with a monthly service charge of $1.00. Express the monthly cost as a function of minutes called.

b. At 0 degrees Celsius, the speed of sound is 350 meters per second and it increases by 0.2 m/s for each increase of 1 degree Celsius. Express the speed of sound as a function of temperature in Celsius.

c. A helicopter takes off from the roof of a building that is 150 feet above the ground. The altitude of the helicopter increases by 200 feet each minute. Express the height of the helicopter as a function of minutes after it starts rising.

d. A car rental agency charges $31.00 plus 8 cents per mile for a one day rental. Express the cost of renting the car as a function of miles driven.