can someone explain this problem?

Emily sells chickens ($14) and ducks ($12). On Thanksgiving day, Emily's total sales were 1080. Ppl bought 3 times as many chickens as ducks. How many of each did Emily sell?

Puzzling2015-01-21T06:20:11Z

Let c be the number of chickens sold (at $14 each)
Let d be the number of ducks sold (at $12 each)

Equation 1 - Emily's total sales were $1,080
14c + 12d = 1080

Equation 2 - People bought 3 times as many chickens as ducks. Or stated another way, the number of chickens bought (c) was equal to 3 times the number of ducks bought (d).
c = 3d

Substitute the second equation into the first:
14(3d) + 12d = 1080

Multiply:
42d + 12d = 1080

Combine like terms:
54d = 1080

Divide both sides by 54:
d = 1080/54
d = 20

Now compute c:
c = 3d
c = 3(20)
c = 60

Double-check:
60 chickens x $14 = $840
20 ducks x $12 = $240
Total sales = $1080

Answer:
60 chickens and 20 ducks