John filled his car gas tank with 21 gallons of gas. He paid $54.39. What was the price of 1 gallon

Solve this system of equations. 12x − 18y = 27 4x − 6y = 10

When y’all answer can y’all explain too !

Barney & noblet customers can choose to purchase a membership for $25 per year members receive 10% off all store purchases 1. how much would a member pay per year if he bought $50 worth of items each year? 2. write a slope-intercept equation that expresses how much a member pays per year using x to represent his purchases per year 3. how much would a member have to spend per year to pay off his membership fee?