The total cost of 5 shirts and 5 windbreakers was $300. Tina bought 7 such shirts, 5 such windbreakers and a cardigan for $405. If the total cost of a jumpsuit and a shirt was $66, find the difference in cost between the shirt and the jumpsuit.
Let 1 S be 1 shirt.
Let 1 W be 1 windbreaker.
Let 1 J be 1 jumpsuit.

5 S + 5 W = 300 --- (1)

1 S + 1 W = 300 ÷ 5
1 S + 1 W = 60 --- (2)

1 S + 1 J = 66 --- (3)

7 S + 5 W + 1 J = 405 --- (4)

(4) - (1)
(7 S + 5 W + 1 J) - (5 S + 5 W) = 405 - 300 
7 S - 5 S + 5 W - 5 W + 1 J = 105

2 S + 1 J = 105 --- (5)

(5) - (3)
(2 S + 1 J) - (1 S + 1 J) = 105 - 66
2 S - 1 S + 1 J - 1 J = 39
2 S - 1 S = 39

1 S = 39

From (3)
1 S + 1 J = 66
39 + 1 J = 66

1 J = 66 - 39 = 27

Difference in the cost between the shirt and the jumpsuit
= 1 S - 1 J
= 39 - 27
= $12

Answer(s): $12