Help elementary school math problem: 3 ducks, 2 chickens for 56 yuan, 3 chickens, 3 ducks for 69 yuan. Do you know how much a chicken costs?
Think about it. 3 chickens +3 ducks, 69 yuan.
2 chickens +3 ducks -56 yuan
————————— ———————
1 chicken 13 yuan
Is this vertical subtraction only the price of a chicken, so it is 69-56 = 13 (yuan)?