Thread: Algebra word problem

Easy word problem: If 6 gallons of premium unleaded gasoline costs $15.54, how much would it cost to completely fill a 15-gallon tank?

The answer is $38.85. Take the 15.54 divide that by 6, then multiply this by 15. But how do you write this in an algebra problem using x? I don't have a clue. Help!

x is how many gallons you pump