Answer:
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.