A car with 15 gallons of gasoline drives 420 miles until the tank is empty. Write a linear equation that describes the amount of gas left in the car, y, after driving x miles.

Step-by-step explanation:

The car uses 15 gallons of gasoline to drive 420 miles.

(15 gal)/(420 mi) = 1/28 gal/mi

The car uses 1/28 gallon of gasoline per mile.

y = mx + b

When x = 0, at the start of the drive, the car has 15 gallons of gasoline.

y = mx + 15

Then for every mile it travels, the amount  of gasoline goes down by 1/28 gal. For x miles of travel, it uses 1/28 * x gallons of gasoline.