you fill your car with 15 gallons of gas for $45. using fractional notation, how do you write a proportion that shows how much 5 gallons of gas will cost? use x to represent the unknown cost
$45/15 gallons = x/5 gallons
$45/15 gallons = $3/gallon
$3/gallon * 5 gallons = $15
So, 5 gallons of gas will cost $15.