The total cost of 7 shirts and 7 windbreakers was $392. Tina bought 9 such shirts, 7 such windbreakers and a cardigan for $492. If the total cost of a dress and a shirt was $66, find the difference in cost between the shirt and the dress.
Let 1 S be 1 shirt.
Let 1 W be 1 windbreaker.
Let 1 D be 1 dress.

7 S + 7 W = 392 --- (1)

1 S + 1 W = 392 ÷ 7
1 S + 1 W = 56 --- (2)

1 S + 1 D = 66 --- (3)

9 S + 7 W + 1 D = 492 --- (4)

(4) - (1)
(9 S + 7 W + 1 D) - (7 S + 7 W) = 492 - 392 
9 S - 7 S + 7 W - 7 W + 1 D = 100

2 S + 1 D = 100 --- (5)

(5) - (3)
(2 S + 1 D) - (1 S + 1 D) = 100 - 66
2 S - 1 S + 1 D - 1 D = 34
2 S - 1 S = 34

1 S = 34

From (3)
1 S + 1 D = 66
34 + 1 D = 66

1 D = 66 - 34 = 32

Difference in the cost between the shirt and the dress
= 1 S - 1 D
= 34 - 32
= $2

Answer(s): $2