Tanner is picking three varieties of apples at an orchard: Gala, Fuji, and Jazz. Each type of apple has a different cost per pound. He knows that 1 pound of each apple variety would cost a total of $5.16, and that the cost per pound of Jazz apples is the same as the combined cost per pound of the Gala and Fuji apples. Tanner picks 12 pounds of apples, including 3 pounds of Gala and 5 pounds of Fuji, for a total cost of $21.24. If g represents the cost per pound of Gala apples, f the cost per pound of Fuji apples, and j the cost per pound of Jazz apples, which system of equations represents this situation?