While on vacation, Rosa stopped at a souvenir shop to buy keychains and refrigerator magnets for family members and
friends. Keychains cost $2 each, and refrigerator magnets cost $1
each. Let x represent the number of keychains that Rosa bought,
and let y represent the number of refrigerator magnets.
Rosa bought 12 items and paid $18 more for the keychains than
for the refrigerator magnets.