x: number of tickets it takes to ride a roller coaster
y: number of tickets it takes to ride the bumper cars
Derrick used a total of 16 tickets to ride the roller coaster 4 times and the bumper cars 2 times, that is,
4x + 2y = 16
Javier used a total of 12 tickets to ride the roller coaster 2 times and the bumper cars 3 times, that is,
2x + 3y = 12